I also -love- making giant stompy robot conversions, and am constantly on the search for the perfect all-bot list.
I don't think traitor legions brought much to the table, as none of the chaos walkers really benefit from legion rules (be nice if brutes got votl), and none of the legions themselves really lend themselves that well to walker-heavy builds (either through synergizing rules, or army composition). Even Iron Warriors sort of suck at fielding walker armies.
Some of the best chaos walkers are daemons, so if you're comfortable making use of them your options open up a lot.
Some staples I've settled on:
Soul Grinders are life. Soul Grinders are love. Soul Grinders are THE workhorse chaos walker. They're pretty cheap, and have great armour, hullpoints, and offensive capabilities, with some customization in daemonic alignment. They can either go fast (slaannesh), go shrouded (nurgle) or go cheap (khorne). They basically ignore shaken/stunned, have a 5+ invul, and can deepstrike to boot.
Even with the subpar daemonengine statline (3's across the board), their sturyness and reliability more than makes up for it.
And now they have a spanking new formation in the daemonic incursion book: 3 grinders that get rerolls to hit/wound when one kills a model per phase. Let's you just plug them into any list without needing daemon
HQ/troop tax, and the rerolls go a long way to solving their statline problems.
Personally, I'll almost always have at least one grinder in a walker list, if not the formation of 3.
Blood Slaughterers are another champ walker. AV13 and a deamon save makes them pretty sturdy, and they're nice and point-affordable. They're similar to the grinders, but they have way more assault potential (WS5, I4, rampage, rage++, and fleet) at the cost of some durability (less hullpoints and AV12/10 on the backs/sides) and ranged firepower. They're also sort of fiddly to control with the old rage rules needing to move towards the closest target, but they'll mulch basically anything in the game so it's not much issue. They can also come in squadrons for some hullpoint mitigation manouvering, and can pack harpoon guns to actually get into assault on the turn they deepstrike. And they should always deepstrike, as it lets you just cram them into the enemy backline and not worry about them getting kited around, chasing squirrels.
Maulerfiends are awesome because they're fast and chew through vehicles really good. They're also a little frail with AV12, and can get bogged down fighting infantry with only 3 attacks and WS3. If you're going to use them, I'd run at least 2 because one will always draw fire and die. Or worse, get immobilized, like mine ALWAYS does.
Hellbrutes are eh. They got better with the
FAQ to give them 4 attacks base, but they're still pretty mediocre with their light armour, low shooting power, and lack of any daemonic saves. I sometimes use the mayhem pack as a cheap "walker troop" unit, because theyre not that expensive and can cause some trouble. Yes, they are unreliable. Rolling the table every turns inevitable rolls the thing you don't want. But they're fun, and they do force the opponent to pay attention to them because they will mess things up in combat. I will say for the mayhem pack to always give them a ranged weapon, just so just can make use of the fire-frenzy roll when it happens, isntead of just sitting there doing nothing.
Now let's talk about the others!
Contemptors: Very killy and decently survivable, but holycrapexpensive. A properly equipped and marked one costs as much as a land raider. Also they have no real mobility aside from cramming them in a dreadclaw (which can eat it). They're cool, but I'd not say they're worth the points.
Decimators: Roughly equivalent to the contemptor. Little more choppy, little more mobile with deepstrike, and little more durable with the resurrection gimmick. But also expensive as a landraider, so... meh.
Ferrus/Sonic Dreads: Basically fancy helbrutes with almost double the cost. The only half-decent one is the siege ferrus dread (which is essentially a chaos ironclad dread), but its also way too espensive, and the other daemon engines do the same thing for cheaper and better. Give these guys a pass.
Forgefiends: If you want Hades autocannons or ectoplasma, take
CSM rapier batteries. They're cheaper, more durable, and more accurate.
For synergy units, daemons are the best bet. An allied detachment for an
HQ with the grimior of true names (3++ daemon save on a grinder is no joke!) and troops with icons/instruments makes deepstriking in grinders/slaughterers very accurate.
love the the bull and just the levels of blood 
