For me, it'd probably be a toss up between Goldberg and Rhino, sometimes spelled Rhyno.
When Goldberg hit the spear, it looked like that he'd use his hands to sort of help pull a guy's legs out from under him when his shoulder connected with their mid-section. Their legs just sort of flying up in the air helped to really sell the impact of the move.
In the case of Rhino, he has a thick and compact frame that's ideal for an impact move like the spear. Rhino's about 5'9" and about 250 pounds or more, so he had a low center of gravity coupled with that thick frame with especially thick, powerful legs that could gave him a great deal of push, especially within the confines of a wrestling ring. When Rhino hit the spear, you could see that he was really putting all his weight and drive into it. The guy taking the move looked like he was damn near taken right out of his boots.
I'd probably have to go with Rhino. As I said, Rhino's natural body type and the amount of force he was able to generate made it an ideal move for him to use. Given his relatively short stature, a move like the spear, or Gore in his case, gave him a real sense of strength that other power moves, like maybe a powerbomb or chokeslam, wouldn't really convey.