I think in terms of graphics in sport games, you're not gonna see a huge difference between the 360 and PS3. Since EA will port their games to PS3, 360, and PC (and sometimes Wii), they're not going to be taking full advantage of the PS3's capabilities. In fact in the next 2-3 years, I think we'll be lucky to see 12 games that actually use PS3 to it's limit. I would say for the short term, go 360 since it's cheaper and has a wider range of games (although like 3 in every 4 games released is the same FPS lol. Also keep in mind that I don't own a 360
But if I had to choose, I would go that route.
And actually... you may wanna wait a few more months for the console prices to drop too. Rumour has it that PS3 is gonna reduce their price by $100, and if that happens chances are you'll see reduction in prices in the 360, and possibly the Wii as well to maintain the competition.
Edit (and slightly OT): Madden '08 for Wii is coming out soon and previewers think it will be fantastic.