What slot machines have the highest payout percentage? The Ugga Bugga slot machine game has the highest payout percentage, at 99.07%. The second highest is Mega Joker by NetEnt, with a 99% RTP. Jackpot 6000 by NetEnt and Uncharted Seas by Thunderkick come in second and third, with RTPs of 98.8% and 98.6%, respectively.