I do think DWade is his best comparison. He will not be as good as Wade, almost certainly, but they have similar strengths and weaknesses. Wade has (had) the edge in athleticism, of course, but Smart might have more point guard skills. Smart might develop his 3pt shot as well as Wade has, or he might not.
Smart will be a great defender for sure, and if all goes well offensively he could peak not far below Wade-level great.