I'm happy playing Guild Wars and I'd recommend Guild Wars instead of WoW or Rift, but to answer you original question... hmmm...
I'd go with World of Warcraft. I haven't played WoW since the Burning Crusade days and recently Blizzard gave me a free week to play (hook me) again and I liked what I saw.
The starting zones were drastically changed with the Cataclysm and they are a lot much better now, each zone has it's own story arch with it's own characters. I was just bursting in laughter when I reached Azshara, at the north of Orgrimmar. It was already a low level zone for me, but I just couldn't stop doing the quests that zone had to offer. You'll fall in love with the goblins and their shennanigans. Riding mechs while killing elves, talking to an intelligent raptor, saving goblins on a beach, Private Ryan style, making a tower explode and then escape just seconds before it explodes.
I was seriously considering into returning to WoW, but there was only 1 gripe that reminded me why I stopped playing in the first place, the money. Right now, I just can't afford to pay $15 a month, but if I had the money, I'd gladly return to WoW. At least until Guild Wars 2 comes out.