Which carrier has the fastest data for iphone 5?

Simple mobile or straight talk?

Added (1). I live in long beach ca. I plan to buy iphone 5 at&t and then unlock it

Both use the same networks, but the answer to your question can vary by location.

StraightTalk is what I would recommend. SimpleMobile has 4G but it won't be supported on your iPhone 5 as the bands are not supported, you won't even get 3G. You'll have 3G on StraightTalk as they don't have 4G LTE capability yet.So, if you want 3G, got for StraightTalk.

I'm using at&t.