as Texan notes, mallards will work on almost any duck...even redheads.
My preference is to "match the hatch"...so if your areas are teaming with pintails, be sure to have some in your spread - - or whatever you are seeing alot of. If you can afford only one species, then I would start with mallrds here in North America....then as seasons go by, increase your spread with the common species in your area.
For example...her in NH and ME we do not have many snow geese, but on occaision we get a lost soul, so my field set for Canadas has a single snow mixed in. Just trying to have a little edge on the competition and add a bit more realism.