Hi-Point 9mm Carbine.. or S&W M&P 15-22... ?

I'm looking at getting a cheap Assault Rifle to go in my Zombie Preparedness Kit... They are about the same price, but curious if anyone has any experience with either of these... I like the look of the M&P 15-22 more, but I'm worried about the power. I don't know if the 22cal with have enough gusto to take down a nasty Zombie... I'm pretty sure the 9mm would have sufficient power, but ammo is more expensive... thoughts??? :)