It depends on the year of the car...If your's is a 1997, get a 1997 motor. If it's a 1998-2003, just try and grab one with the lowest miles you can find/the best price.
There is no difference in motor between a sedan and a coupe. Just try and find a clean, old lady driven donor...which would imply sedans are better, since little old ladies dont drive coupes XD.
Best bet is a low miles, babied Regal..but anything L67 will work.