speedster on 4/19/2012 3:44:26 PM:
IMO, either will be fine.
I personally use road-oriented, tour tires, with basic treading on them, but nothing elaborate is required.
If its absolutely pouring rain and getting soppy and soft, the slightly wider, heavy-treaded cyclocross would make out better, but honestly, people waste too much energy on here worrying about tire choice, if I'm to speak frankly about this issue.
The C&O is a very run of the mill trail surface and not some trials/downhill mountain bike course. That said, I wouldn't necessarily advise doing it with a narrow, untreaded race slick either..so just use common sense and you'll be fine.