Should I buy a US amp ax3000de or an Alpine MRP-M2000?

It depends on your setup really i personally like alpine products. The difference between the two is the alpine will run 2000 watts rms at 2 ohms, and the us amp will run 3000 watts at 1 ohm. look at how much power your subs need and at what ohm load your going to run them, base your decision off of this. If you have 2 subs with dual 4 ohm voice coils you can run them at 1 or 4 ohms, or if you have dual 2 ohm voice coils you can run them at 2 or 8 ohms.