Gregor Clegane vs Maelys the Monstrous

On one side, the near 8 feet tall Mountain. Inhumanly strong, wearing the thickest plate in the seven kingdoms, a greatsword in one hand and the shield in the other. Also said to be quicker than one would expect for a man of that size. He did (essentially) get bested by Oberyn Martell in the trial by combact but Oberyn himself is a really skilled warrior and at one point Gregor's greatsword came mere inches from getting him anwyay.

On the other, Maelys the Monstrous. He fought his cousin Daemon for the command of the Golden Company, killing his destrier with a single punch and then twisted Daemon's head until it tore from his shoulders. Crazily strong and savage, he was eventually slain by Barristan Selmy and that gave Selmy undying reknown in the kingdoms. At 23 Barristan was named for the Kingsguard.

1v1. Who would you bet on?