I'm from Western Michigan, with a lot of the area actively farmed...
Farming: Almost exclusively John Deere, especially in the larger and newer equipment. Once in a while I'll see a Case/IH, Massey or White, but not very often - unless it's older. There are a few newer pieces of NH equipment starting to show up now.
Also, there are a lot of miscellaneous older tractors running around on hobby farms and such, just about every brand and color you could think of.
Contractors: Small tractors are usually Kobotas with John Deere being runner up. Again, I'm just recently started seeing NH boomers being used by contractors.
State: Generally state-owned equipment is painted orange in Michigan, though I don't know if this is always the case across the state. It is almost always Ford. Contractors who contact work from the state generally seem to use John Deere.
Heavy equipment: Caterpillar and John Deere are most common with a smattering of Case and different Japanese equipment. The Japanese heavy equipment does seem to be becoming more common over the last few years.
Observation - as someone else alluded to, I suspect the dealer network in a particular region has a lot to do with the sales patterns.
In my own area, John Deere is very well represented by good quality dealers. NH has a few, but not as big or slick as the JD dealers. Kubota has a few scattered about, and Case/IH doesn't have a dealer for miles around. Massey isn't very well represented at the dealer level either, though I do know of a dealer about 20 miles away.
There's probably a cause and effect at work here...
*** REAL horses weigh a ton ***