I'm not super impressed by either Okafor or Towns. Okafor has a decent offensive game, but doesn't get good postilion all the time and gets pushed out a lot, which for the first couple of years in the NBA will happen a lot.
Every time I try to check out Towns, he's on the bench, and a lot of the time during crucial parts of the game. He also looks more like a PF than a center. Which he may be a nice upgrade over Sully. But I don't see him as a rim protector.
I'm sure the C's will put them threw the tests if they get a chance and maybe the defensive ability is there for Okafor, he's just never had to learn it in highschool and it's showing in college.