Well it depends what you want to do with your army, and how you want to play it.
Personally I favor mobility, which means lots of Wave Serpents for my troops.
I'm currently fielding 2 full squads (getting a 3rd soon) of dire avengers, as I love their shooting ability a LOT over regular Guardians. Depending on my point size, one or both is joined with a Farseer (guide+doom+bladestorm=game over) and all of them are mounted in a Wave serpent, so they can bladestorm . . . kill everything that could even have the slightest chance at assaulting them, embark, and move.
In another Waveserpent I also like having a full squad of Banshees (take em up from 6 to 10) to wreck the enemy's
CC and elite squads of infantry.
Fire prisms are
IMO the best ranged Eldar tank poppers available, there isn’t much that a twin-linked
str 10
ap 1 shot can’t take out, unless you are unlucky
now some interesting thing I’ve noticed with the point costs in elites, points wise, a full squad with an Exarch of Dragons=Banshees=Scorpions, mounted in a wave serpent you could swap them out depending on your opponent (can't do this in tourney's, so you best choose wisely).
Scorpions and their insane number of attacks I find do really well against "horde" armies of Orkz and Nidz
Dragons and mean against Armor Based Iggy, and the combination of Flamer+tank-killers makes for a quick way to deal with troop-filled transports
And banshee's power-weapons are excellent against all forms of elite
CC, with a squad I’ve easily taken out nobs, terminators, and pretty much any unit without "fearless".
Oh, there is nothing more aggravating to an enemy than a full squad of pathfinders . . . in cover, on an objective (yay 2+ cover save!)