Wow, is -this- thread going to get out of hand quickly. I'll try and give you an answer close to the top before it gets crazy. I have played both. I only play Guild Wars. That should pretty much sum up my bias.
Firstly, the games aren't similar in gameplay:
Guild Wars is essentially Diablo 3, combined with a trading card game (like Magic: the Gathering) as far as what skills and such you have.
World of Warcraft is just the latest incarnation of the Everquest model of MMORPG. If you take WarCraft III, and the three-map campaign that was released with Frozen Throne but explode it to about five million people and zoom in really close on the map.. that's World of Warcraft.
Secondly, no game has a monopoly on friendly or unfriendly people. It's the internet. EVERYONE is unfriendly! This is because they think you can't find them and punch them in the neck. Sad, but true. Gods know I've tried.
So, why would I recommend Guild Wars to someone instead of World of Warcraft? Just on general principle:
1) No monthly fee. You can play just on weekends and not feel like you're wasting money.
2) Easy-to-reach level cap. The game moves along very briskly. You don't have to wait forever to be awesome, you get there pretty quick.
3) Instanced adventure zones. Never have to worry about your target being killed by someone else; never have to worry about being killed by a twelve-year-old who just got a D on his report card (or the twentysomething who has no life and takes it out on you).
Also, World of Warcraft is a poorly designed game, and is not fun. Guild Wars, baby! XD