for me that honor goes to the game , for which i have played for over 4+ years now and still going strong.

FINAL FANTASY XI:ONLINE

just love the auction function,partying with ppl from around the world,the city factions,mission,quests,summons,crafting,almost every aspect of the game i truly love and still do. the only thing i dont like is the death delevel if u dont have enough exp.

Guild Wars: Free, able to create a party with your friends or computer controlled characters, and it hasn't gotten boring after over 500 hours in.

Diablo II Lord of Destruction. My favorite free RPG. It places few restrictions on character development and does not require team play.

Halo multiplayers--There is nothing funner in the world than playing one of the halo's multiplayer wether it be online or with your friends.  And constant updates, and maps ensure you never get bored.

Best multiplayer game this world will ever see.

Easily for me, its World of Warcraft. Very close second Ultima online.

WoW, I think everyone knows what Wow can make some people become. Talk about addiction.

As for UO, it was my very first MMORPG, and I have been a big Ultima series fan, so for me it was a can't lose scenario.

Guild Wars was a great one for sure.

But i'd say it goes to WoW in the long run.

Gunz The Duel is STILL a great one to play to, a PS3 version only makes it better.

Starcraft, for sheer balance and its wicked custom maps.

Starcraft is still awesome to play online.

WoW

D2 LOD on Battle.net

Wc3 original (before TFT)

Yes this... I can't believe I forgot Starcraft...

I really meant Starcraft + Broodwar. But semantics :)