MATT W. - Interesting question, I think the best answer is what NOT to get, as William said, Originals are neat, but are THE odd-ball CC.
I'm not real fond of Quiet-Lines, the rubber mounted engines and side panels, bendix style starter and elec. PTO clutch was all introduced on them. BTW, it was the ONLY IH tractor that the engine was rubber mounted in, which should imply something.
But anything from a 70/100 to 86/1X8/1X9 and all the red tractors, 482,582,682,782,982 are all good. I'm partial to gear drives since the rearends are just about impossible to tear up.