I think there's actually four types.
Deep V, think big lake craft, 16-18' high sided Lunds etc. Made for deep water, heavy wave action, tough lake boats.
Low V, think '50-'60's V boat runabouts, 12-16' low sides. Meant for oars or low HP engines, thin hulls, miminal ribs. Not great in deep wave action with the low sides, not tough enough for grinding over rocks etc.
Flat bottom, basic utility or pond boat, blunt nose, no deadrise at the transom, good for flat water, streams, marshes, shallows etc.
Mod V, basic flat bottom with a pointed nose and slight deadrise to handle better at speed vs. a flatbottom.
Under the right conditions any of these types will work in the other styles waters but each type fits different uses better.
Jamie