If you are looking for trigger response, you want a high torque motor, not high speed. Although I think that's what stealthmaster14 was trying to say since AMP doesn't sell a high speed motor under their brand.
Yeah, all those brands I mentioned are pretty much the same thing. A lot of people believe they have the same OEM. I forgot the AMP is only high torque.
The G&P M160 and M170 motors are also good choices, but they are really expensive and the performance won't be that much better than the ACM motors. (the M160 might even perform the same)
Depending on what battery you use, you may get pre-engagement with a highspeed version of the motors I posted earlier, you should probably go high torque.