Xbox 360:
Many many many games. Good Games.
Best online play and worth the $42 (or something like that) per year.
PS3:
Most games are also available for Xbox 360 and only a few exclusives worth mentioning.
free online play but no fun extra perks. (again you get what you pay for).
Blu-ray is amazing. In fact so good that HD DVDs are non existing now.
PS3 is more expensive
And as far as game gaphrics go. There are vary few recognizable differences.
So unless you really really really want the blu ray I suggest Xbox 360. But that's just my honest opinion.
Edit: As far as lagg. You'll experience it no matter where or on what console you play. Online is still online