Having played a total of 6 games of NewHammer, I'm an expert. Trust me.
. In this rating system, colour will signify my general rating.
Blue equals great, the best of the best, and the reason to take psykers in any kind of list.
Violet equals good, and are either situationally powerful, or are potent build-around powers.
Red are powers to be avoided, and if you are being forced into taking them perhaps you should be reconsidering even having the psyker.
Hereticus Astartes Psychic Powers:
Infernal Gaze - In most ways, Infernal Gaze is a worse Smite, but one that's occasionally very effective to have. Whereas Smite always deals at least 1 mortal wound, Infernal Gaze can deal 0 mortal wounds. The important part is that it can hit any target in range, and not just the closest! This makes it helpful at taking out low-level characters, or already wounded characters, that would otherwise be protected by their meat-shields. Can also be used to take off the last wound from a vehicle in a similar situation. However, most of the time, Smite is just more reliable, and it requires things to be just right to have Infernal Gaze work, though it'll feel great when it does.
Warptime - Warptime is just about the most solid psychic power you can take. While it doesn't have a long targeting range (only 3 inches), the ability to move twice is one of the strongest in the game. Furthermore, unlike the Swarmlord's Hive Commander ability, Warptime doesn't impose ANY restrictions after its use! You can go ahead and charge, shoot, or even use psychic powers as normal, making it incredibly versatile. It's also not the most difficult spell to get off either, only requiring a 6. There's hardly a Chaos Space Marine list in existence that doesn't benefit from this power.
Prescience - Adding 1 to your hit rolls is very useful, especially since so many Chaos units hit on 3's normally. This conveniently also effectively removes the penalty on moving and shooting heavy weapons, or shooting at Hard to Hit units. The only reason it's not
Blue is that it's difficult to get off, needing a casting value of 7. Remember for this that due to the way triggers work, adding 1 like this eliminates the penalty for overheating plasma guns, and causes your Death to the False Emperor ability trigger on 5's instead of 6's (or on 4's if you have an Icon of Excess!).
Death Guard Psychic Powers:
Always remember for Death Guard that you can take regular Sorcerers in their army list, and these Sorcerers will still have access to the Hereticus Astartes Psychic Powers, meaning that you can combine them together! Theoretically you can do the same with the Nurgle Daemon powers, though you'll be restricted to only use these on the Daemon Prince, Foetid Bloat-Drone, and Defiler. Fun-fact, these three units are also both Hereticus AND Death Guard units, meaning they can benefit from ALL THREE disciplines at the same time!
Miasma of Pestilence - Making your forces Hard to Hit (effectively) has become a top-tier ability. Any penalty on shooting is made extra-penalizing against abilities like this. Woe be to those Space Marines using Power Fists or Thunderhammers against a unit under the effect of this spell.
Gift of Contagion - There's only one good result in this list, and that's the Liquefying Ague (-1 Toughness). There are times when the other two will be useful, but you need to be hitting a close combat specialist unit for that to happen. Combined with the difficult-to-cast warp charge value of 7, and you have a power that rarely goes off, and rarely does what you want it to do. If it could reduce a characteristic to less than 1 to prevent blob-squads like Cultists or Termagants from making any attacks in close combat, then it might be a bit better, but you're better off avoiding this.
Plague Wind - Death Guard got the shaft on a number of psychic powers. You need to get a really sweet roll against a really big squad for this to be any better than a smite. Again, the only useful thing it's got over Smite is the ability to hit units that aren't the closest. Perhaps with a longer range so it could hit backfield blob-squads, then it might be better, or if it did mortal wounds on 5's, then it'd be great and worth it sometimes just for that extra almost-Smite.
Tyranids:
The Horror - You'll try to get this off every turn, but it can be difficult to target the right unit with this, as their power powerful ranged abilities are often past 18 inches away. Still, reducing a large squad of accurate fire, or units with a ton of firepower, from 3's to 4's or 4's to 5's is super useful, and it's also useful if you run against another powerful close combat army by making their attacks far less accurate.
Catalyst - When don't you want to make your stuff even harder to kill? The only hard part about this spell is figuring out which unit will need it most, and putting it on the Swarmlord is pretty much never the wrong thing to do.
Onslaught - The only reason I don't use this so much is because the other two powers are just so effective. The other reason is that you only can use it AFTER having already ran a unit, meaning you're making a much bigger risk than with the other two powers. For that reason, I tend to only use it on a unit that is not otherwise going to be able to shoot or assault anyways. That's not a terrible thing, especially if you combo it with the Swarmlord's ability, but you need a plan when using this power.
That's it for now! I'll expand this list once I try more stuff, but in the meantime, what would you grade your powers as?
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UPDATED July 25/2017:
Craftworld Eldar - Runes of Fate:
Eldar are interesting in that they have two disciplines, but Farseers can only take from the Runes of Fate, and so far I haven't used the others, so you just get these. Of note for ALL Craftworld Eldar powers in this discipline is that they go off on a 7, but the Farseer is able to reroll specific dice from a single manifest attempt, meaning that the Farseer's ability to get off 7-value power is very similar percentage-wise to a regular psyker's ability to get off a 6-value power, and is in fact about 1 or 2% better than that, but only for one power that they would otherwise fail to cast that turn. So, despite these warp charge values being higher, I am going to grade them kinder than higher ones of other faction's.
Craftworld Guide - Guide is useful in that the Farseer can hide very easily, yet still throw this charm to friends that are far away. Unfortunately, it only helps their ranged rolls, but that's not too shabby for a faction that's tended to shine brightly in the shooting phase. Put on a vehicle or monster with lots of heavy guns, and you will get some good bang for your buck.
Doom - Whereas Guide tends to be better on your big heavy weapons, Doom is better for your smaller weapons. Rerolling to-wound rolls with Shuriken Cannons and rifles vastly improves their chances of getting those critical "6 to hit" rolls to trigger their armour-shredding capabilities. However, this power forces your Farseer to become a bit more exposed, especially to counter-charges. I'd only take Doom if I was on a bike for this reason, and so it gets my lowest rating of these powers. EDIT: Upgraded to violet!
Fortune - Despite not combo'ing with other Feel No Pain powers like almost every other race, Fortune is still a powerful ability to have, especially when used on a Wave Serpent that reduces the damage it takes. You can also stay nicely hidden while throwing this power around, but it's hard to get off for what it does.
Harlequins:
Twilight Pathways - This power is effectively a slingshot. With a very reasonable casting power of 6, you can mostly reliably get it off, and making a unit move twice when they can run, shoot, and charge while also Advancing (like twice due to this power) with already insanely high movement values lets your unit cross unimaginable distances blisteringly fast. There is something very odd about it in that the wording seems to suggest you can't Blitz with a Solitaire and use this on it in the same turn, but it actually says you can't use Blitz if the Solitaire was targeted by this power in the
previous psychic phase, so according to this wording, you can move with the bonus
3d6" from blitzing and advancing, then be targeted by this power, or move your advance
d6", then when targetted by this power advance and blitz.
Fog of Dreams - When all your opponent can see are dancing clowns, this power becomes good, but I almost graded it red because of how narrow that application is. You need to get real close with your opponent (not hard for Harlequins admittedly), but it's nice in that a very powerful enemy unit will become worse against your whole army in that all-clowns situation. If you're only taking Harlequins for a couple units, then this power instantly becomes
red as your opponent can mostly ignore it.
Mirror of Minds - In theory this can one-shot Magnus himself off the table, but more often than not you'll deal 1 or 0 mortal wounds. If you absolutely need some extra Smite-lite for a power that will fail to go off more than 50% of the time during a game, be my guest.
. Also notice that Librarius Discipline can affect any loyalist Astartes, which means your Tigirius can cast Veil of Time on Space Wolves Wuflens, so they will be like being affect by their own Hunt curse, and then also cast Might of Hero on the 
