PS3 is still plagued by the YLOD issue once a while, and dead lens problem
Not sure yet if the slim version solved these issues.

Xbox360 wise the failure rate (3RROD) USED to be very high, until recently with the release of Jasper set, which claims to have solved the 3RROD issue. Until now after the launch of Jasper set more than 10 months ago, haven't heard any one kena such issue anymore.

Game library wise, both are almost equal in strength, but Xbox360 are having the slight upperhand for now.

and of cos, PS3 has the upperhand in media playing, eg: Bluray

Online multiplayer wise, I would say both are equal in strength, albeit one need to pay subscription for online multiplayer, and one is free. But xbox live is more govern, monitored and stable according to some.

and if you are still undecided, get a Wii then