I did it. I made the decision this past Monday in the matter of 10 minutes lol. I walked into a store, told the woman I wanted to switch to you guys and she ported the number over and everything. She was being a little too casual with me and she told me she placed my preorder, after us speaking about it at least a couple of times. I called a couple of hours later because I didn't receive the EIP email yet and lo and behold, she really didn't place the order (dummy). Anyway, she had no problem porting my number over. AND the unlock request was accepted in about one minute (seriously). Very easy transition.
I spoke to AT&T about cancelling service and they said it was already canceled when T-Mobile ported my number over. I was like okay, cool, no more work for me haha.