I've had a few favorite zones in my time.
Befallen -- a beautiful looking old world dungeon. Interesting set up with varoius keys in different places. The well sucks tho!
Kael Drakkel -- something about killing giants is just fun. Sucks as a gnome though =(
Temple of Veeshan (mainly entry and the middle room) -- Just looks great. Walking around waving at dragons is fun too :)(Ssra is nice too, but haven't been there much).
City of Mist was always a favorite of mine. Decent exp in the mid-low 40s, and just fun to hang in. Haven't been there much since revamp though.
I could go on and on about favorite zones, but I will quickly finish :).
Other favories include: Paineel (it's a great city), Hate (if you don't count the lag), Najena (fun low level place), Karnor's (just to sit at zoneline and watch the train fest.), Nadox, Dulak, Stoneburnt (nice and peaceful, used to spend several hours there killing, and would be lucky to see more than one other person in zone the whole time I was there), The Hole, Charasis is a beautiful zone as well (though I've only spent one evening there), Veksar, and more that I've forgotten.
My all-time favorite though, is ToFS. I absoultely love this zone (should go back more often..ahh the time). Esthetically it is beautiful, both inside and out. The keyed aspect makes each floor feel like a different zone. The exp and drops here are pretty good for the level, and the difficulty is right where it should be.
Feen's Small Text List of zones he doesn't like: Crushbone (/ooc drama), PC (/ooc drama, poor grouping/personal skills), Highkeep (same as above), OT (boring as hell), DL (boring as hell, PC 2.0), PoJ (basement and caves are ok, other ones are bad), KC (hunting here sucks...PC 3.0), PoStorms (never got into this zone...just find it boring), BoT (PC 4.0, getting into towers now, which are new and nifty...but the wing camps are boring)