The spanish website Meristation makes a comparison between the 360 and PS3 versions of the GTAIV game. The comparison takes into consideration all of the aspects of the game.
It afirms that the PS3 version of the game has superior AA filter, better HDR, less loading, better controls (with great use of the Sixaxis) and solves the framerate drops without any difficulty, contrary to the 360 version which this causes a little more problem.
While the 360 version has Downloadable content and achievements, not available on the PS3 version.
In the end, the article goes to say that, if you have the option, go for the PS3 version.
Translated version on the Credit URL.