I would say:
Truck Fest 89 diesel racers, 7500 spectators
Thunder in Muncie 200+ racers, 3000+ spectators
Englishtown has a truckin nats 1100 racers ?? spectators (this race is frustrating as a racer, good on attendance)
TS Performance All Diesel Challenge 100+ racers, 500-800 spectators
Like I said about Englishtown, that goes for all of the Big Rig races I have attended, with the exception of Truck Fest. I was impressed with the quality of that show. The one's at MIR suck, just because the track officials are asses. Depends on your goals, name saturation for the sponsors or quality races for you.