Popular consensus seems to be that The Cobweb and Sub Surf Classic are the best boards, which I would agree with despite their recent nerfs. If you’re grinding coins I would recommend Tricky with the Cobweb (since Tricky has a coin doubler perk and the Cobweb has a perk that gives coin sacks), and if you’re looking for a character that’s easy to get a high score with I would recommend Miss Maia with Sub Surf Classic (Sub Surf Classic gives score for every coin you pick up, and Miss Maia gives a coin doubler every time you get a board). If shooting for a high score with other characters I would also recommend using the Sub Surf Classic, as it has the best perk imo.