The
B7800 is a "basic" tractor, the TC33D is a "deluxe" tractor with more features and also has more horsepower. I can't comment on the JD and how it compares. I can tell you that I own a Kubota
B2910 which is sort of a deluxe version of the
B7800 and I really like it, but I also own a NH TC24D and while it is much smaller than my
B2910, I think it is a better designed tractor with lots of very nice features than the
B2910. I think you may have a hard time comparing the TC33D with the
B7800 because the TC will have more features and more power.
As for the Kubota engines, they are excellent.
If you are doing a lot of loader work, it is impossible to compare the extra visibility that you get with the TC series tractors to anything on the market. The TC has a sloped and curved hood that makes forward visibility excellent. Kubota has big flat hoods that block visibility. Deere has big flat and wide hoods that are even worse for FEL work than Kubota's hoods. I say this, after spending the better part of last week clearing an industrial field with my Kubota and its FEL and I never realized how bad the view is up front until I spent a lot of seat time working only with the FEL. That made me a real believer in the NH hood designs for FEL work.
As for pulling a mower, any one of them will do the job just fine.