My two favorites are Everquest and DAOC. I just have so many memories with them and it seems that every time I try to play a new one I don't make it past the first thirty days. I had so many fun moments in those games and moments when I was pissed, but as that saying goes, "the sweet ain't as sweet without the sour."

I will always remember the first time I discovered an entirely underwater Zone in Everquest. You had the feeling of flying as you swam. I played for five years before I was able to move on, and I have friends that are still playing Everquest today(6+ years.) The depth of the content in Everquest is still staggering.
After five years though I was ready for a simpler diversion. I have come to love the streamlined elegance of City of Heroes/City of Villains.

Everquest classic. The addition of the plane of fear and hate were cool imo. Also, Naggy/vox. Following EQ Classic, the game really dropped the bar though. I think aspects of atleast kunark was neat. But, people give it far too much credit really. Velious really ruined what the game had once been.

I thought Kunark was a decent expansion. I agree, Fear/Hate were awesome.

After Velious EQ just lost its damn mind.

world of warcraft is probably the best MMORPG ever made. best isn't always the funnest, however. I had just as much fun playing The Realm, with it's shitty 2d graphics and horrible trading system. Ragnarok online had the very best online economy I have ever witnessed in an MMORPG. pure genius. everquest was very immersive. WoW is nice and balanced - that is good and bad. I've certainly logged more hours on WoW than anything. The Closed Beta of WoW was much, much funner than the current retail release.

I've played AC, EQ, DAoC and some EQ2 and Guild Wars as well.

DAoC was clearly the best game I played. The RvR in DAoC is unmatched by any other game.

Played quiet a few.

AC
AO
Shadow Bane
Everquest 2
Herorizions
Planetside (well mmofps)
EVE online
few more :)

best for me was AC :) Just cause it was the orignal one for me and I played it for the longest time (ermm about 3 years). I get very bored of the other quickly :(

Eve Online !!! - It's just amazing and fun.
And best thing about it that even if it's slow u can play it whenever you want, when you have time.. skills can be in training even when offline.

http://www.eve-online.com/