Really, I would try and test out the exclusives, I mean both offer great games. Although, if you want to share an experience with your girlfriend PS3 is great, there is LBP, Flower, and PS Home is very popular with the girlfriends of the guys who own ps3. A guy I know had his PS3 utterly taken over by his wife because she loves Home.
If you are a fan of unique games, you should look into Flower on PSN, Heavy Rain is also coming out which is promising a brand new feel on gaming, last and certainly not least PS3 has Valkryia Chronicles.
Could anyone suggests any games that are targeted to both genders and non gamers on the 360? I am not very up to date on them.
PSN ID: KingFate_