Best Amp Possible for $275

hey guys, im planning on upgrading my system soon, and i want to see if u guys can suggest any good amps for me

for the moment.. because i haven't decided on a subwoofer, i dont care about the ohm load.. but it needs to make.. around 500-600rms, also im going to shy away from hifonics, lanzar and any of the "bang for ur buck" amp brands for the moment.. because although they probably work well. im skeptical, so i don't mind paying a lil bit more $ for better quality equipment

i have a few amps in mind.. tell me what u guys think..

Memphis 16-ST500D
Memphis 16-PRD500.1
Crossfire VR600D
Alpine MRD-M501

any other amps? i will greatly appreciate suggestions!! thank u

What are you powering with the amp?

not sure yet, so ohm loads dont matter, i just want to know whats the best i can get with that $$, i'll decide the sub later, and most likely my sub will be sealed, so ssf isn't a requirement

well u should decide the sub first then get an amp..... check out some avionixx 800.2's I got a 1200.2 and LOVE it....it would be hard to find a new one but used shouldn't be a problem.