Okay not even close. GT5 is better by a long shot. It 's more real, fun graphics are better and the gameplay is too. The PS3 controller is made for TPS, Fighting games and racing games. It's like comparing a used car to a new car. Which one would you take if they were both the same price?
As far as sim racing, yes, I think GT is by far the better franchise (thus GT5 is the better sim). On the other hand, as a game [overall], that's where things start to become much more even on the playing field (with Forza actually topping GT in certain aspects).