1) SanDisk. Whatever card you buy, it's worth the extra few dollars to buy a SanDisk. (No, I don't work for them, but I've contacted them and I have cards of theirs that date back to the days of the first SD card and they're still working. The only bad one I ever had was one I cracked. It still works, but I'm afraid it'll fall apart if I try to take it out.)
2) Since the phone does 2160p video, a U1 card is just a bit too slow, you want a U3 card if you're going to do full 2160p to or from the card. If not, a SanDisk U1 (or Class 10) card will be fast enough.
(I don't buy anything but SanDisk. Even though anything important is backed up to at least one hard drive and one cloud account, I don't want to have to replace the card, then copy everything back to it.)