Moving past the stats that suggest otherwise, having used both, and understanding their values...The Prowler has a lot of Edge on the Vanguard at any range. Assuming similar loadouts, 2/2 or 1/2 crew, the Prowler has the advantage. Why? Lockdown. If you're far enough away that you don't have to worry about getting rushed, use it. If you're so close and have a Vulcan Gunner, use it. The Shield is cool, but you'll chew through that thing.