You said your sub was a dual voice coil, 2ohm sub right?
That means depending on how you wire up your single sub, you'll have either a 1ohm load or a 4ohm load.
From what I can tell, the MA Audio amp is not 1ohm stable, and therefore you would have to wire in series and run it at 4ohms, and it's only 400w RMS @ 4ohms.
The US Acoustics is the better amp of the two, especially since it appers to be 1ohm stable, however it's only 300w RMS @ 4ohms.
What is your sub rated in terms of peak and RMS handling?