Welcome to Android Central! I don't have any of those, but based on lots of comments and reviews I've read, I'd probably remove the M9 from the list, since the camera seems to be universally regarded as mediocre. The S6 and the G4 are probably your best bets. G4 has a removable battery and a microSD slot, while the S6 doesn't, so that would sway me more to the G4 side (and I'm also not a fan of TouchWiz).