Gas - Kawasaki, Kohler, Honda - the rest just don't matter.
Diesel - Kubota (RTV), Yanmar (JD 4310) & 7.3l Turbo (Ford F-250)
As for working on them - if they don't break, you don't have to worry about how difficult they are to repair. Just maintain them like you'll keep them forever. My Cub 1450 is older then my kids and I didn't have to send it to college:laughing: