I personally hated Guild Wars. I was looking forward to it for so long, and it just is not a very good game in the long term unless all you want to do is pvp. If you are really into team PVP, get it and you will love it. However the game is really limiting if you just feel like playing by yourself one day and exploring. Your characer will never get good enough to actually explore past the first couple cities witout dieing constantly.
I'm not a big fan of WoW, but if you don't necessarily want an MMORPG I would look into Diablo 2. It is very old, but still stands up to the test of time with the new patches here and there that totally change the game. It is free too, the only con is that the servers tend to lag sometimes.