Lucas Marine - found that it hangs around better & doesn't wash out / get hard. Wife got me the DeWalt powered gun a while back...that's been really nice. I bought the lock-n-lube fittings a few years ago. That made it even better.
You are correct; tractors work in adverse conditions and withstand extreme impacts and vibrations. I grease daily when tractors and implements are cultivating and planting, and grease is cheaper than replacing the gear.for the tractor, i don't obsess about the grease type, just frequency of lube.
i've found over the years that grease hardens & can be a bear to break loose.
so time interval is just as important as hrs on the machine between lubes
as a footnote, i've found Lucas marine grease resists hardening over time & moisture conditions