Rotary works is a color packer and a half. Get the 12volt motor. It needs less amps and is more compatible with power supplies. I have a one off one piece rotary works ( no give ) and it colors fast.

A good metaphor for amps vs volts is this:
Say you have a motor that runs 9 volts at say 0.5 amps. No think of that as a single lane road with 9 cars. You can get this 9 cars 1 at a time safely and there won't be a problem getting 9 more through afterwards.

Now say a 2amp Motor at 6 volts. Now you have a 6 lane highway and can take 6 cars at once. Now your power supply has to provide all 6 cars at once. This can be taxing as some power supplies have a 2amp protection circuit.