So 26" fat tire is going to be like a 29" standard tire.
Watch a YouTube video on 26" VS 29" tires and why 29" is smoother.
In short, 20" would be terrible on any trail that is not paved. If you have suspension on the 20" it'll help but my assumption is that there is no suspension.
So for smoothness on the trail, the 26" fat tire will cushion the trail and make it somewhat enjoyable.
The problem with hub drive is burning out the drive. If you have any hills that you're try to pedal up with your hunting gear, your drive system will do it but it won't be happy. That's when the perks of a 20" tire kicks in. Smaller tire = easier to drive.
If you can find a mid drive with 26" fat tire you'll be happy.
I built my own. Norco bigfoot fat tire bike with a bafang middrive bbshd.
I am in British Columbia Canada. My bike goes up steep, logging roads with me and 25-30lbs on my back with no issues.
In short:
20" will rattle your fillings but will delay you burning out your drive system
26" will be smoother with better grip but if you live/hunt in the hills or mtns your drive system will hate you.
Good luck
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