Ugh, if you seriously are asking this, you don't belong in this forum. Obviously AT&T has nano sims, obviously Verizon. They're the official LTE carriers. Anyone else is TBD....
T-Mobile claims they will have nano-SIMs sometime next month. I have not heard about any of the AT&T MVNOs such as Straight Talk, but I'd imagine they'd get them in soon. Do you have an unlocked AT&T or a Verizon model? If you have a subsidized AT&T model you'll need to get it unlocked before any other SIM would work.