Ignoring the fact that Battle.net has been a cesspool of pure idiocy for the last 10 years, Blizzard just doesn't impress any longer. Also it is unlikely that PvP will be comparable to Diablo II, which is still one of the few games with a decent PvP system.
Guild Wars is completely different from WoW, other than the fact that they're both MMORPG. Rather than grinding endlessly, you do events that pop-up when you're in their specific area (You also gain exp/gold dependent on your involvement, so you can just hit once and get experience).
The World v World PvP is suppose to be amazing (I focused on PvE the last beta weekend as I was seeing if my girlfriend would want to play or not). So far, this is the only game that has been exciting to me for more than a few days as they do things much differently than other MMO's. One complaint though is that the 'personal storyline' isn't really dependent on user choice, and you're more stuck with specific paths with only a few flags to modify the storyline. It's also entirely possible to solo the game (I did the whole 1-20 storyline on a level 18 necromancer).