Have ordered BF3 for the PC and will be playing MW3 on my PS3. I have two completely different sets of mate I game online with on the PC and PS3. Not wishing to sit on the fence but I am looking forwards to both.
I'm also looking forward to both. MW3 will be a thrill-a-minute ride that is well polished and will delivery huge amounts of fun as long as it lasts. BF3 will be deeper than that. But there's still pleasure to had in playing both games.
I'm probably more excited about MW3 than BF3. The only thing I find satisfying in FPSs anymore is running around with a sniper rifle and MW3 looks set to please on that front.