To be honest, I think Gears Of War will be better.
It's the best Xbox 360 exclusive, while Resistance 2 is far from the best PS3 exclusive.
Although they have worked hard on Resistance so it can be a great game too.
But Gears of War is at the top with a Press Rating of 9.6, whereas Resistance 1 has a 8.6.
Anyway you never know, look at this, it's so harsh for xbox fanboys:
http://answers.yahoo.com/question/index?qid=20081027045158AAI1DAp&r=w