The 351W would be your best bet. Most available performance parts and is affordable. Factory heads are restrictive and has a solid block. Toss on some aftermarket heads with a decent intake and let her rip.

The 351C is next but takes a little bit more knowledge to make them go. Decent flowing heads but block is cast weak. Back cylinders distort on an engine stand. Only the 4v heads are good but takes a good custom cam guy to make them a monster from idle to 6500 rpm. Wrong camshaft makes the lowend soft.

351M isn't really worth it. Might as well make it a 400 but by the time you correct the camshaft and boost the compression you would be ahead of the game with a 460. Same exterior engine dimensions and gets the same mileage.