I moved from a
B3030 to a 3720 so i think i can offer some input, as far as capability, there was a vast improvement, much more control and stability for a given load. Plowing snow and grading gravel roads go much better as well.
stability may be a wash as i found the 3030 to be tippy and added wheel spacers (on the 3720 just flipped the wheels)- which were almost a requirement for chains. At first the 3720 seemed tippier(perhaps due to operator seat height/ but in reality it has not started to actually pick up a rear wheel whereas the 3030 seemed a bit prone to it. one direction it may be less stable is fore and aft where the much greater fel capacity is not fully compensated for by the 3 inches of addl wheelbase. With either i would not operate them without filled tires ( and preferably something heavy on the back- in fact my dealer fills the rears on on compacts they deliver.
with regard to operation and owning i found a lot of little ergonomic features on the jd that i have come to appreciate- things like the folding rops set-up that does not vibrate and is easier /quicker to deploy (i store in a garage)
I found that i grew to like the 2 pedal hydro set-up but it took a while and really is not better, just different YMMV.
moving the brakes to the left however has been really useful, just last night i used them when trying to scrape the drive with the fel while my 1000 lb snow blower was raised- i need to get some front weights
I can fit the jd into almost any place that i could the kubota , i had considered moving up to a 4X20 but think that storage and maneuverability might then be an issue
I attached a couple of side by side pics- the kubota has its front blower in the bucket