This might be a little out dated now, but this is something we threw together on another forum just after 6th dropped. Most of it still holds true.
(apologies for wall of text)
6th Ed. Necron Codex Report Card
Note:
S: this unit is so good it is considered auto-include for many armies.
A: pretty damn awesome unit, worth making room for.
B: not bad at all, would probably be worth your while taking, if you can spare the points.
C: it's okay. I'd still look at some of the other units in the category before choosing this one.
D: uhh, there are much better things out there, man... but if you insist, don't say we didn't warn you.
F: don't even consider using this (unless you've worked out some hitherto unrealized combo with this unit)
HQ
Imotekh the Stormlord = A-
He causes long-term night-fighting, and makes lightning strike your opponents units... though he's pretty expensive. Only consider him for big point battles.
Nemesor Zahndrekh = A+
He gives incredible bonuses to your guys, and takes bonuses away from your opponents guys. All for only 5 points more than a similarly equipped generic Overlord! Pretty awesome, if you can afford him.
Vargard Obyron = B+
Has a S7 power weapon, is WS6, and can teleport his unit from one side of the board to the other, even if they're locked in combat! THE Necron close combat master. He does not take up a
HQ slot if you take him with Zahndrekh, though the two of them together are quite pricey. Works very well with Lychguard. Not an Overlord level Necron, so can't take a Royal Court.
Illuminor Szeras = F+ (C- if combined with Anrakyr)
Give one unit of Immortals or Warriors a randomly determined bonus. Carries Assault/Defensive Grenades, so that's not too bad. He's a Cryptek, so can't take a royal court.
Orikan the Diviner = D (C+ if combined with Necron Airforce, C- if combined with C'tan)
Can grant your reserve rolls re-rolls. Also, on the first enemy turn, causes the entire battlefield to count as difficult ground. Occasionally known to hulk out for brief moments of time. He's a Cryptek, so can't take a royal court.
Anrakyr the Traveler = B-
Can hack into enemy vehicles and control their guns, allowing you to shoot your opponents guys in the back with their own Vindicator. Grants any unit he joins Counter Attack, so not bad with Lychguard. Can also upgrade one unit of Immortals with Furious Charge and Counter Attack.
Trazyn the Infinite = A
Can wipe out hordes with his
CC weapon. Comes with Mindshackle Scarabs. If he dies, you can have him come back as another unnamed
HQ, Lychguard, or Praetorian. Is also scoring.
Generic Overlord = A
DIY
HQ is actually one of the most versatile choices you've got. Most people give him a Warscythe and stick him on a Command Barge to go hunting vehicles.
Destroyer Lord = A+ (S if leading a unit of Wraiths/Praetorians)
Another close combat powerhouse. Grants any unit he joins Preferred Enemy. Give him Mindshackle Scarabs and stick him at the head of a unit of Wraiths for one of the 'Crons most vicious Deathstars. Can't take a royal court, unfortunately.
ROYAL COURT
Lord = B+ (A if kitted out properly)
Give him a Resurrection Orb and stick him in a big unit of Warriors to increase their survivability. Give him Mindshackle Scarabs as well as a Warscythe, and you've got a pretty decent combat Lord that will fit in well with Lychguard.
Generic Cryptek = C
His 3 shots at S5 AP3 are pretty good, but a little short range, so act as an assault deterrent. Upgrade him to a Harbinger, however, and you'll be able to grant your units all sorts of buffs.
Harbinger of Destruction = A- (A+ if given Solar Pulse)
Carries a las-staff. Solar Pulse turns the lights on or off for a turn, giving you precious protection from long range enemy guns. Can also give a unit defensive grenades.
Harbinger of Transmogrification = C (B if given Crucible)
Carries a staff that can cause any enemy unit hit by it to be in difficult terrain in their next movement phase. Crucible makes any enemy unit trying to assault your unit take a -D3" movement penalty.
Harbinger of the Storm = A (S if attached to small unit of Warriors/Immortals in a Nightscythe)
Haywire staff shoots short range lightning that will wreck any vehicle in the game, so long as you don't roll a 1. Lightning Field makes any enemy unit attempting to assault your unit take
D6 S8 AP5 hits.
Harbinger of Eternity = D- (B+ if given Chronometron)
Staff is a close combat weapon that is garbage. Chornometron lets you re-roll any dice once per phase for the unit he is in.
Harbinger of Despair = C+ (S if leading Deathmarks. S+ if also given Veil of Darkness)
Staff is a S8 AP1 flame template that uses Leadership value to determine to wound. If used with Deathmarks, that staff becomes an AP1 auto-hit weapon that wounds on a 2+ against one chosen enemy non-vehicle unit. Veil of Darkness lets you teleport the unit he is attached to around the field.
TRANSPORT
Catacomb Command Barge = A-
Used to be borderline broken, now just fairly good. Pretty much death to any vehicle it flies over, thanks to its Sweep Attack rule. Sweep range was nerfed in 6th, but making it a Chariot makes it more survivable.
Ghost Ark = A
Can only be taken by Warriors and
HQs. Can replace fallen Warriors in squads. Good for either keeping next to big blobs of Warriors to keep their unit restocked, or used as a gunboat for shooty Harbingers + 5 Warriors).
Night Scythe = S
Best transport in the game that also happens to be a flying Annihilation Barge. If it is destroyed before the occupants disembark, they go into reserves instead of taking crash damage. The only reason you wouldn't want to take multiple of these is if you're trying to play "fair".
TROOPS
Necron Warriors = B
Either have them in big blobs with a ResOrb Lord and/or Ghost Ark in support next to them, or split them into many multiple small groups to have them jump in Nightscythes, or to have shooty Harbingers attached to maximize target acquisition. Beware, they have a tendency to get swept in close combat. While they can glance vehicles on a 6, try not to rely on this as your main source of anti-tank. (pro-tip: try to include one extra unit of 5 Warriors in every list for late-game-walk-on-from-reserves-objective-capturing. This tactic wins games).
Immortals = B+ (A if upgraded via Anrakyr)
Tougher than Warriors, with better guns. Basically a Space Marine who can get back up after dying (not a bad ability for only one point extra). Still pretty bad at close combat, though. Can take tesla guns, with inflict an extra 2 auto-hits if a 6 is rolled when rolling to hit.
ELITES
Deathmarks = A (S if accompanied by Harbinger of Despair).
Rapid fire Snipers who can deep strike (but no way to mitigate scatter). Can wound any one chosen enemy unit on a 2+. Attach Harbinger of Despair for insanely cheesy combo (just be aware you gotta get close for it to work, so stick them in a Nightscythe).
Lychguards = C- (B if lead by a combat ResOrb Lord + Assault buff Harbingers)
Necron close combat dudes. Can take either a S7 AP1 weapon, or a S5 AP3 power sword with a shield that grants them a 4++
inv save, AND has a chance to reflect incoming fire back at the firers. Downside is their speed. Either need a Night Scythe or a Veil of Darkness to get them into combat. Better as mobile cover or Assault deterrents for your other vulnerable slow units.
Triarch Praetorians = C+ (B+ if lead by a Destroyer Lord)
Jump infantry with decent power weapons. Can be given Entropic Strike weapons too, which can be handy against vehicles, as well as pistols for a second attack in Assault.
C'tan Shards = C (B if abusing rules via powers and unit synergy combos)
Monstrous Creatures that have a pretty vicious stat line... but you're really taking them for the powers they can take. See codex.
Flayed Ones = D-/F
Lots of attacks for cheap, but aren't able to have Royal Court members attach. Yes, they can deep strike/infiltrate, but then just sit there getting shot. The 5th edition codex update kinda wrecked these guys. Really, they should have been troops.
Triarch Stalker = B- (A if taken in pair)
Multi-melta dreadnoughts. Any enemy unit hit by this model will have twin-linking AGAINST it (‘Cron long range guns LOVE this guy). Attracts a lot of fire, though, but that's not so bad, as it will distract your enemy from shooting at your other stuff.
FAST ATTACK
Canoptek Wraiths = A+ (S if lead by a Destroyer Lord)
'Cron assault unit of choice. S6, Rending, 3++
inv save, Fearless, jump infantry, ignores all terrain tests, can reduce initiative of enemies in base contact to 1. No Reanimation Protocols is the only downside to these guys.
Canoptek Scarabs = A-
Eats tanks... no, literally, it eats armor (if a single Scarab so much as hits a vehicle, said vehicle loses an armor point on the roll of a 4+). Dies quickly to templates. Used to be auto include in 5th. Now, with all the anti-
AV options 'Crons have available, they've kinda taken a back seat.
Tomb Blades = B
Fast, excellent weapons... but just not as good as the two units above. Cheap as stock standard, but can get pricey if you give them all their best upgrades.
Necron Destroyers = B
Excellent at killing Marines. Not bad, just not as good as most of the other options in the Fast Attack slot.
Heavy Destroyers = B-
They've got good range, but they're a little over priced. (for the price of one, you can almost afford 2 Harbingers of Destruction. The debate rages over which is better). Preferred Enemy for shooting really helped these guys.
HEAVY SUPPORT
Annihilation Barge = S
90 points for a gun that fires 4 times, but scores an average of 5 hits? This thing is AWESOME! Also good for anti-air defense.
Canoptek Spyders = A-
Monstrous Creatures that poop out Scarabs every turn. Look up "Necron Scarab Farm" for cheesey combo. Can repair your vehicles and give them back their precious hull points. Also great to spam for Smash attacks.
Doomsday Ark = C+
Great range, really powerful... but extremely vulnerable, in that you have to hold still to get the most use out of it.
Doom Scythe = B+
S10 AP1 gun that auto hits anything under a
3D6 inch line... unfortunately, that
3D6 line can't hit fliers (but the Tesla Destructors still can!). Has to start game in reserves. If you're going to take one, take two instead.
Monolith = C+
It used to be incredible... now it's just okay. AV14 means there aren't many things that can hurt it, but a deep strike scattering onto a Guardsman can potentially lose your death pyramid. It's simply no longer the invincible tournament winner it used to be. The vacuum ability can be hilarious, though.
and why?
)
): 9/3 
- 3000pts Rampagers 
