There seems to be a bit of argument between flat or lenticular but it seems to boil down to how shrouded your frame is, as the deciding factor for whic one you use.I've not really found any evidence to suggest there's a huge amount of variation between discs whereas front wheels seem really sensitive to frame, fork and tyre choice. The trick is to find someone fast with your frame and copy them.
My aero head says in free air a lenticular disc is more aero, but as soon as you shroud the front of the wheel with a close-fitting frame you're just adding more frontal area with the bulge. In that case, a flat disc ought to better. This is all in a straight line, too. Add yaw and it's probably different.