Hawks, meh, weak shots but can take out tanks with Haywire, but there are better choices in that slot.
Scorpions, pretty good, they pump out a lot of attacks at high initiative and have a marine save and S4 in CC
Banshees, ick, just ick, if you REALLY want a CC unit these are not the way to go they still are only S3, they have an AP but it doesn't really make up for it
Spiders godly, no other way of putting it, they simply kill EVERYTHING, get some, now
Spears again, meh, better choices in you Fast Attack slots (may i remind you of spiders) they are like light cavalry, they kill on the charge but then crumble subsequently
Dragons popular belief is that they are very good, I personally don't have a lot of luck with them, but if you're going to take them your best bet is to get them in a Wave Serpent and get them up quick to take out vehicles and heavy infantry.
Crimson Hunters if your meta has a lot of flyers, its great at taking out those, but they are starting to dissapear from play now because EVERY army has some way of dealing with them in their new books
Dire Avengers Most people are only taking these to run serpent spam these days, guardians are generally better for your points
Seers Farseers and Spiritseers are AMAZING, warlocks, less so but I am a big fan of them myself, boosts up the Guardians very effectively.
Autarch Current rules they are pretty good, they are especially useful if you have a lot of reserves just to make extra sure they do or do not come in.
Eldrad Not as good in this edition due to the cost, but kind of terrifying still
Avatar Expensive, and CC based, not really the point of Eldar
Phoenix Lords Most are only decent, but Asurmen is actually pretty good, he can do some nasty things to people in any phase.
Illic He's kind of for giggles, not good, not bad, but if you want to run rangers or pathfinders he can add some punch to them.
Yriel Tooled up Autarch, I've seen him be played but again, he's designed for CC
Wraithguard With the D-Scythes these guys rip things apart, moving them close to your enemy is never a worry because they are high toughness high save and if you get charged 5d3 shots on your overwatch (I've had opponents nearly cry when I told them that)
Wraithblades I don't like them, but high toughness, high strength and multiple attacks is pretty useful.
Wraithlord CC unit, funny thing about them is they can challenge, doing that against a Sergeant is PRICELESS
Wraithknight Take him bare, charge him into combat, win, move on.
Grav tanks Falcon, BAD, do not get, Fire Prism, alright good against almost anything, Wave Serpents GET MORE, I dont care how many you have, get more.
War Walkers oodles of fun, thats all there is to it, oodles