Air:
UNSC. Broadswords with energy shields, and Pelicans with M8C Grindell/Galilean Nonlinear cannons (AKA Spartan Lasers) would dominate.
Armour:
Rocket turrets and Gauss cannons will easily penetrate the armour we have today. They also have the mammoth for transporting vehicles and loads of marines, and it's armed with Rocket Turrets.
Infantry:
You only talked about the MA5C. Some of the Assault Rifles have far superior range and accuracy, e.g. the MA5D and the MA37. It's not just Assault Rifles, we also have the Battle Rifle and the Designated Marksman Rifle for longer range battles, and the SAW can shoot pretty far when fired in short controlled bursts
Special forces:
SPARTANs and ODSTs. 'Nuff said.