Listening to them both really highlights the strong arrangements and production that Jan used. The Beach Boys' backing tracks are pale in comparison to Jan and Dean's. It is only when Brian started using Hal and the Wrecking Crew that we start to get that strong rhythm and driving sound that Jan initiated.
That said I like Dennis' vocals on Custom Machine. He brought an edge to the vocals that contrasted so well with Brian's. Pity he wasn't used more.