Played both a lot, personally i liked Guildwars better, better story, and a lot more fun. But WAR is okay too, but still a bit buggy.

Guildwars:
+No monthly fees
+Great Story
+Fun quest

-Not really a mmorpg

WAR:
+Fun PvP
+PQ are a lot of fun

-PvP does get bored fast, well scenarios do get boring
-Monthly fees
-Buggy