My favorite game, and MMO, to date has been Perfect World International.  Their flight engine was (and is) amazing.  It is literally THE most underappreciated MMO I've ever seen.  In my humble opinion, it blows World of Warcraft out of the water (especially because it offers everything WoW does for free and even has nicer graphics).  I have a level 101 cleric named SeriaKaltya. She's my favorite to play, but there are several other unique classes like Stormbringer, Duskblade, and Venomancer. 

In short, PWI is the closest MMO I have ever found that resembles Sword Art Online. (In case you're wondering, it's run through the Arc client.)

A close second as far as favorite games go would be Heroes of the Storm, but my ancient laptop will no longer play it (or Battle.net in general). 

P.S.:  You're conversing with someone (me) whose only WoW charrie was a level 4 blood elf who got lost near spawn.  If PWI can make me stay till level 101 and WoW can't, that's saying something. >,>