There are several schools of thought on this. In the real army, typical front line infantry carry light weight, low caliber, relatively low rate of fire, low range weapons. And a side arm. But that doesn't translate to the nerf hobby very well. All Elite blasters are light, they're all the same caliber, and unmodded Nerf® blasters all have the same effective range in their respective class (RIVAL, Elite, ULTRA, etc). So your only variable is the rate of fire, and to some degree the capacity.
The unofficial NIC roles are Offense, Defense, Scout, and Commander. So infantry falls solidly in the Offense role. The suggested offensive loadout is a springer primary, and a multi-shot secondary. Some playbooks suggest an optional single shot tertiary.
In reality, it's difficult to carry a decent secondary like a Disruptor or a Scout without a proper holster. So if you're outfitting a whole club, then that's going to be an issue because shoving a Disruptor under your belt is extremely uncomfortable.
As far as springer primaries, the Retaliator is king. (Personally I don't like the Reta, but that's another discussion) Other good springers are the Alpha Trooper, Delta Trooper, Recon MK/CQ, and the Rampage.
But some flywheelers are also good primaries for the assault role. The Stryfe, Modulus, RapidStrike, and Infinus are perfectly good primaries, although they lack stealth. But they bring higher rates of fire which is often important in the infantry role.
And for a tertiary, just give everyone a Jolt.
My personal Assault loadout is a lightly modded Alpha Trooper (100 FPS), a holstered Strongarm, and a Triad, with a thigh pouch that holds four CS-18 clips, and a nerf vest. That gives me 99 rounds ready to go, plus another hundred loose darts in my vest.
