If the 03A3 is in good shape and you've shot it enough to get to know it, I'd use that one. It'll use any commercial .30-06 hunting ammo with no sweat. The Enfield should be .303 British, which would also be swell, unless it's a WWI American Enfield. I can't remember exactly what those were called (Pattern 14?), but that's likely .30-06.
.30-06 can be loaded with bullets from 100 gr. to 220 gr. and several different powders, for whatever shooting you want to do, probably one of the most versatile calibers ever made.
Might as well use the rifles you already have, IMO. But I'm a Cheap Old Bastard too.