The M4 definitely. Been way too long since it's been in a GR game. Gonna put an Elcan SpecterDR ("Digital Scope" in the game), Magpul AFG, PEQ-15, suppressor, and 30 round mag on it. Maybe occasionally swap between a standard and short length barrel. Hopefully there will be a couple buttstock options, since I don't care for the fully-collapsed CAR stock.
SCAR-H is a close second, while my go-to pistol will naturally be the M1911A1.