Jim,
Since you asked; You will not find a better Auction Company than Mecum. I have over 20 years experience with them.
As far as which Auction to go to and when should your cars go across the block, we'll there are many factors which come into play.
Timing, logistics, type of car, the Venue, your budget, the value of your car .... etc...
General Rule; The sooner you can consign, the better. This way you get to Maximize your exposure (Marketing for the vehicle).
I have been to the K.C. Auction and the Sell Rate seemed Very good to me. IMO anytime you can sell more than 50% of the cars crossing the block, in a reserve auction scenario, then I feel the Auction Company has done a very good job.
The Consignment Directors at Mecum ALL have loads of experience and can help you make the best decision for you and your car.
ps Rockford/Belvidere/Boone County fairgrounds was a very good venue, but it has been replaced with a better one, The Indianapolis Fair Grounds. (All indoors and no tents!!)