AMT makes some nice small handguns, but I'm not sure how much they'll grow. But, if you were to ask about Hi-Tech, invest in Cisco. Cisco has an 85%+ Market Share. Seriously, there is no real way to know which guns people will buy, unless some company comes out with something radically new. But, then again once its banned, your screwed. Possibly, Olympic Arms. Oly Arms has low prices for AR/M4gery Parts. Fulton Armory has some nice accesories/upgrades for ARs/M4gerys. Kel-Tec has a nice Carbine (Sub-2000) and might grow. But, the amin decider is price.
Good Prices:
Hi-Point
Kel-Tec
Olympic Arms
Moderate Prices:
AMT
Fulton Armory
Bushmaster
Armalite
Blue Chips:
Beretta
Glock
Ruger
S&W
Colt
Mossberg
Norinco (If You Want To Support China, Commie Bastard)
H&K
Fabrique National (The Europeans Seem To Love 'Em. Especially Their Crappy Single-Shot (Non-Semi Automatic) M4gerys.)