I'm currently on AT&T, but planning on switching to T-Mobile soon. There's also a possibility that I will switch to Verizon at some point in the more distant future as well, so ideally I'd like a iPhone 6s that works on all 3 networks. It seems that the AT&T version is the best to buy since it includes 30 Band LTE. Is there any benefit in buying the other model? Is the AT&T version missing anything that the other one has?