If you look around, you can probably pick up both guns used and only pay a little more than you would for either one new. Try 'em both, decide which you prefer, and sell the other for what you paid for it. I would bet you won't be selling either any time soon.
Both guns have there advantages. I like the GPR because it seems to shoot well at near the maximum load with round balls, the sights, are great with either the fixed or adjustable rear sight, and it looks a lot more authentic. I prefer the weight and balance of the T/C, and the shape of the butt plate is much more comfortable for me. It is also an accurate gun with roundballs, that's all I ever shot out of the one I hunted with years ago, and although it probably would be hard-pressed to beat a GPR in a match, it is more than adequate for hunting.
What you've asked is a really tough question and I think you'd be more than satisfied with either choice. In the end I would go with the T/C Renegade, mine is .58 cal., because of the T/C warranty, consistent quality and it's American. That said I liked my GPR but just couldn't justify keeping another .50 cal.
I do have one more thing to add to this already overly long post, but don't neglect the Lyman Trade Rifle either, I think it is probably the best value there is for a general purpose ML. I just wish mine were .54 caliber rather than .50.