Replicant/Mobile Carriers

Who here uses Replicant? I was thinking of buying a Samsung Galaxy S3 and installing Replicant on it.
Originally I was going to buy an S2, but I read something about them running slow.

Then, I would need to put it on a GSM carrier's network, if I'm understanding this correctly.

What mobile carrier do you use with your Replicant phone? I was thinking of going with T-Mobile, Cricket, or MetroPCS, since they have stores in my city.