I'm biased- been running Gleaners since 1976- 4 of them....K, F, F2, M2. Was tempted to buy a JD 6600 years ago- way better, tougher machine than a 4400. Heavier shafts, bearings, etc. But, working on any combine- Gleaner is the simplest. Others stack 2-3 pulleys on a shaft, so when the bearing goes out, you get to pull 2-3 steel pulleys off ( ruining them) to get to the bearing. Gleaner mostly uses cast pulleys. I've counted the drive belts on a xx00 JD, had twice as many as a Gleaner.
HANDS DOWN- BIGGEST ADVANTAGE WITH A GLEANER IS ROCK PROTECTION FOR THE CYLINDER! No one else comes close with their mickey mouse rock traps! RT fills up and the next one goes into the concave! Gleaner just pops the cyl door open, and it spits out onto the ground. Buzzer/light comes on, you get out and check, close the door, and go!
Still, biggest issue is maintenance- way easier to work on.......look at any Massey if you think the reds or greens are tough to work on.
Local custom operator runs JD but told me Gleaner was a better machine........only reason he switched was for the finance plan from the company.
OK- if you're asking about an older machine....you want something easy to work on, easy to adjust, get a good sample from..........you cant go wrong with a good Gleaner. Just check out which machines are available in your area.