OK, here's the breakdown
Guild Wars - In my opinion, the best MMO out there. Very few "collect x object" missions required to go through the storyline. Lots of quests, excellent storylines, good graphics (for an MMO), and no monthly fee.
Runescape - Pretty good MMO. It's had a lot of criticisms for its graphics, but recently has had a major graphics update with the release of Runescape HD and fullscreen options. It has pretty good quests, hours and hours on end of gameplay, and many minigames for the gamer who wants teamwork involved. It has really evolved from what it used to be. The downside is, though, in order to get all the features, you must become a member (which I highly recommend, especially after completing all the free user quests). Membership costs $5 a month, but it does have a ton of new features and updates constantly. Good news is that you can be a free user and try out very much of the game, and if you like it, spend the money on becoming a member (it's less than any other fee-based MMO).
Last, but not least...
Neverwinter Nights 2 - Not an MMO, but pretty damn close. It's an offline RPG that can be played on online servers, and is constantly expanding, due to the fact that other people make modules for it. This is my favorite RPG, It has an excellent storyline, great graphics, different character personalities, and the ability to actually command all of your party, adding a strategy element to it. It costs no money to play online, and can be played on servers hosting many other people (exactly like a computerized version of D and D, the original RPG).
Thanks for taking the time to read my post. If you wish to contact me in the top 2 games, here's my user names:
Runescape - Saiyanpower2
Guild Wars - Urlso Arcanum