It depends what your definition of secondary is.
If it's for when you shoot a mag dry or have some other miss-hap in game then a pistol is the one one have.
If you're talking about something you leave in the safe zone in case your primary has a catastrophic failure then the rifle/SMG is the one.
And as always you get what you pay for and you really want a lot of rifles, pistols, and SMGs just for fun.
Airsoft, where nothing is hurt but feelings.