Assume its a perfect world and we had our pick:
Peppers:
28yrs old
6'7 283lb DE with 12.5 sacks this season, 5 FF, and 44 tackles
or
Haynesworth:
27yrs old
6'6 320lb DT with 8.5 sacks, 3 FF, and 51 tackles
Personally, I'd go with Peppers, since we've got Stroud in the middle, with a decent Williams next to him. Even if we do get Haynesworth, we still have to address the lack of a passrush from the outside.
Carolina has average DT's and Tennessee have average DE's, but we have average DT's and below average DE's. If Peppers has proven anything in his career so far, its that you don't need to have an all pro DT in the middle for him to be successful.
Cut Kelsay, pick up Peppers, and make sure Schobel is still alive, and I think our DLine is a strong one.