a amp that matches the rms value of the speakers your powering.
there really isn't a brand that is better then others-- most are really on par with each other--that, and i hate giving brand recommendations, because there are so many brands, and what works good for me might not be what you really need..
also, as a first poster,i should let you know that this is primarily a site for installing computers in cars, so audio specific advice is a little slim... your welcome to stick around though!
u need to get an 400 rms amp as long its CEA-2006 complant amp it dont matter what amp to get
because you have 2 of them i would get an kicker kv 400.1 its 400 rms at 2 ohms
2005 Pontiac G6
Front speakers:Infinity 6022i
Rear speakers: Powerbass pb-b6.5xv.2
Battery: top of line walmart brand(LOL)
Wiring: 1 run of 0 ga
Amp: MTX JH600 & Lightning Audio B300.4