From what I've heard Halloweekend fridays are the best to go. I know not all the coasters are open, but how are the lines and such on friday nights.
Shockley
The University of Toledo 2010
Raptor Rides-363
Fridays were great last year. Well at least the friday I went. Dragster s wait was consistently under an hour. The actual line was a good size but they were launching trains in under a minute intervals. Millennium Force was a little over an hour. The haunted houses were pretty long. I think Friday would be the best day to go though. Avoid Saturdays at all cost.
Fridays are great days to go, usually. Just be aware that for some strange reason it almost always seems to rain on Friday nights during Halloweekends.