Both types of edges are used by manufacturers. Would appear that a V edge is faster and easier to apply and would provide the sharpest edge for a single use (as most broadheads are lost or damaged). Having said that I myself prefer to use the Steelforce PhatHeads which do infact use a very heavy blade stock and appear to have a convex edge.
IMO either type is just fine for a broad head, there are many other factors that will come into play; type of steel, stock thickness, cutting edge length, etc. A convex might resist deformation a bit better, although it resiting deformation might make the arrow and head deflect more than one might desire. YMMV.