http://kotaku.com/384422/which-version-of-gta-iv-should-you-buy-we-compare-the-ps3-and-360-versions
Another review of GTAIV some interesting things from it.
"The Xbox 360 version seemed capable of achieving a smoother frame rate, peaking higher in certain circumstances, such as in confined spaces or during light traffic, but both versions seemed to regularly run at a similar clip"
"The Xbox 360 version can suffer from some very noticeable texture loading, as things like trees, vehicles and building signs will regularly pop-in as one tools about town. It can be distracting, especially during high speed chases, and the PS3 version isn't entirely immune from it, but it's not a game killing problem."
The two versions are so close to identical, visually, that putting together a comparison was a challenge. Initially, it appeared that the PS3 suffered from more noticeable aliasing than its 360 counterpart, but after eyeballing the final retail copy, they appear to be on par.
If you're looking for more GTA IV, and you may very well be after you've completed the core game, you're going to want the 360 version.
The Xbox 360 version has the requisite list of Achievements exclusive to the platform, creative and challenging goals that sometimes go beyond the regular gaming experience. However, as with other GTA games, stat-tracking for kills, stunt jumps, and the dozens of extras will keep completionists on the PS3 side happy.
The PS3 version has optional SIXAXIS motion controls for piloting helicopters, steering boats and doing motorcycle tricks. You'll probably leave it off, just like I did.
The good news for Grand Theft Auto fans is that whatever platform you have chosen as your own, GTA IV
excels on both.