F2 or F3 with a 4 row head will get you harvested a lot quicker, and will fit any road or gate the 4 row planter goes in.
The orange heads are older, use a lot of chain to run everything, folks kinda dislike them but I ran my orange head for over 20 years, gets the job done. The black headers are shaft driven, a step up.
Nothing wrong with a good K machine, but just smaller, takes a long time to harvest corn...
Gleaner is easy to work on. I have 3 good dealers an hour from me that carry parts on hand. You need a dealer that supports you, combines need parts.......
JD 4400/ 4420 is a nice machine too, tho if the break, its a bigger headache working on them, lots of stuff buried behind other stuff.
Nothing wrong with the red machines, 800 or big 900 series. The newer rotary Red combines are easy to work with I hear, but they are big, and you said you didn't want big.