Judgment Time: The best mmorpg to date is..
Star Wars The Old Republic.
First, some qualifiers.
I started playing wow back in 2006 (the tail end of vanilla wow) and stayed with it until late 2010, it got too stale and boring for me. I've played a beta version of guild wars but my experience with that game is limited, I've played Aion and Rift.
As you can see my mmo experience is by no means exhaustive, but out of all of the games like this I have played, swtor is the best by far. The leveling process is not the fastest, it feels more like my original wow run in terms of level progression time, but it is FAR more enjoyable. Bioware tried to mix in more of their single player rpg elements into the mmo so the main quests are orders of magnitude more interesting than anything in any mmo before this version. The combat is similar to wow, but has enough differences in style and mechanics to make things seem fresh without being a complete cluster @$#% like aion was.
But the mechanics are not where the game shines, it really is the story. People will probably read that and gag on how absurd it sounds, but it really does make a difference when leveling. I do not know how endgame will be, so we'll see, but for not this is the best mmo I have ever played, (currently lvl 32 and so beyond the intro zones).