I currently have an Alpine MRD-M1005 V12 Digital Mono Amplifier and I want to buy 1 12" Type R sub is it better to get 2 ohm or 4 ohm?

 

get the 4 ohm sub and it wires to 2 ohms.

 

SWR-1242D
12" Subwoofer (4Ω + 4Ω)
Power Handling
Power Handling Capacity (RMS): 500W
Power Handling Capacity (Peak): 1500W

IMHO 1000 rms is too much for that sub.

SWX-1243D
12" Subwoofer
CEA-2031 Speaker Rating
Peak Power Output: 3000W
Max RMS Power Output: 1000W

The X would be a better match.

 

Instead of the MRD-M1005 what would be best? alpine MRD-M650 ,Alpine MRP-M650 , Pioneer Premier PRS-D1100M , or a Audiobahn A8001DT?

 

If you already have the amp (more power is a good thing) why not upgrade the sub?

 

The deal for the amp fell through so I don't actually have it

 

Were you looking at new gear or used gear?

 

depend on your amp maximum power .if your amp stable at 1ohm max power get the the dvc 2ohm sub,if your amp stable at 2ohm maxi power get the dvc 4ohm sub.
more amp power is better .i believe your type r can take the power.