both do suck, but the thump more so. one may be a max rating instead of RMS, or at a different load. one may be class AB while one is class D one probably uses much cheaper parts in the construction. many reasons
is there some advise, or a good site to read explaining what to look for in buying one?
I would say the biggest thing is the brand- pick a AMP that comes from a big company (Alpine, JL, Rockford, etc) dont buy SONY though. Also make sure that you know the watts. I mean if its Max Power or RMS power. It will make a big differance. If you get a Max Power they are usually cheaper but say its 1000 watts Max Power, well it will probably never get close to 700watts in its life. An RMS will be a better buy.
I have recently bought 2 vibe space 12" subs that are both 600 watts rms each and together 1200 watts rms. Could any one suggest what amp I should consider using with these subs. Also what power rating amps I should be looking at. Price isn't a factor