Personally I would suggest slowly collecting Playboy Sasuke. While Refines, Coins, and such bring you BP, Playboy Sasuke unlike Konan is never gonna come out of a card flip. when you see him, use your points to start working on him. If you don't spend any money it make take 4-5 events to collect him but in the end he is worth it as he is EXTREMELY powerful because he is a "p2w" ninja. Refines, Coins and such c*l be obtained easily other ways.