I'd say Frags and Bowser tied for me as overall best player, but if I have to spectate someone match I would 100% rather go watch Bowser just because of his playstyle, I can't sit there and watch 4 walls, a spinner and a wall breaker finish an OU match after 40 mins, just no.
In specific tiers, I'd go Bowser for the reason above in OU, Raaidn in UU just because he did show he was the best in this tier when he used to play and it was the only player who could give me trouble building creative teams not made out of 5 walls, I'd go with Frags in NU. Fuck doubles.