They're about the same size. Rampage is probably the stronger guy. He's the better striker. I think Rampage holds his own in MMA wrestling when you factor in strength (He has against Lindland, Henderson, and Randleman). They both have good chins but I think the edge there goes to Rampage.
So, Rampage by better, stronger striking and a better chin.
maxpower, I agree Randy is stronger than Hendo and Lindland, but he's not as good of a wrestler. Randy is not stronger than Randleman and Rampage handled Randleman's wrestling. Sylvia is a big guy but he didn't look great in the clinch, wrestling-wise, against Vera, who is small at HW, and who took him down. I don't think Gonzaga's greco-roman is awesome either. The are big guys though. I'm not saying Randy isn't great at greco-roman, I just think Rampage can hang with him.
I didn't see the Randy/Randleman fight but from what I've heard, and correct me if I'm wrong, Randleman was out wrestling Randy until he got tired.
Goku, I have not seen the yoon dong sik fight so I can't really debate you on that except to say that Rampage was in a rut for a while there and that fight was around that time. The main thing I have to say in response to your post is that I don't think Rampage is weak in the clinch in so far as wrestling is concerned. He's just shown a suseptability to getting his head pulled down in a thai clinch and then eating a few knees. Even if he hasn't fixed this problem I don't see it being a big issue against Randy.