I have guild wars, and World of warcraft.
I played GW for a long time before it got boring, also the no monthly fee was very nice, plus the expansion comeing out soon...
but right now im hooked on WoW, i must say im not into it as much as i was into guild wars though, and the PvP on guild wars is a little too weak.. fad builds own everything and unless your in a good guild, PvP sucks.... dont expect the competiton arenas to give you a realistic idea of the PvP of this game
as for WoW.. 50 cents a day to play is a bit much, for how much time i have... but it is hella adictive..
get both and see which you like better. but if your broke (like i was) then get GW, it is super fun for a while...