The 360 can do some nice anti-aliasing tricks within certain conditions. Overall though the PS3 is graphically more powerful as well as far more powerful in general which allows for more things happening on screen at once and such.
Judge the PS3 exclusives with regard to the PS3's capabilities and how this technology is advancing over the years, with developers claiming lots of additional headroom for future titles. (Super Stardust HD, Uncharted, Ratchet, Resistance 2, Motorstorm 2, Killzone 2, etc)
With regard to cross platform stuff, things are and have been improving as well. For instance Madden 2007 and Madden 2008 360 to PS3 ports were mediocre, while Madden 2009 is said to be vastly improved and a little better on the PS3. Legacy game engines require adaptations for the PS3 technology, which is effort and time consuming, but also multi-platform developers are getting there slowly but surely as the PS3's install base becomes more and more interesting to them.