What SIM card should I use to put my unlocked Verizon Iphone 5c on straight talk?

I just purchased a GSM unlocked Verizon Iphone 5c and am currently trying to put it on straight talk. I've purchased the BYOP kit from walmart and I know I need to use the nano sim but IIm not sure if I should use the at&t compatible SIM card or the T mobile? Or does it not matter? Any feedback would be really appreciated.

It doesn't matter what SIM you should use as your iPhone 5C supports all the bands supported by AT&T and T-Mobile. I would buy the AT&T compatible SIM for better coverage though.