For me, it's without a doubt Shawn Michaels. Not because I dislike Triple H, but I feel like Shawn has had a bigger impact. Despite his size, Shawn quickly rose through the ranks from tag team wrestler to Intercontinental champion to WWF champion. He helped make it acceptable for smaller guys to succeed in the wrestling business. Shawn is one of those guys who can have a great match with anyone, oozed charisma, and excelled in either alignment. He also helped bring many gimmick matches to mainstream wrestling. Shawn got better with age as well, and Triple H started to become repetitive with age IMO.
But hey, I'm biased.