I don't think the L's are available with mid PTO, so you can't put a MMM (belly mower) on them. You would need to use a rear finish or rough cut mower. Both will otherwise use similar 3pt hitch equipment, although as you go to the larger L's, you can go to bigger equipment. Although some on this site like the RFM's, especially because they are easier to remove from the tractor, I like the MMM because I can work it around obstructions better and can remove it from my B in less than 5 minutes so I don't consider it to be that big of a deal.
I have a B2920. On the 3 acres we live on, it is bigger than I need and could easily do most anything I need to do with a BX. We own an additional 12 acres that is a mix of woods and pasture. I could easily mow it with a BX, but the B is better suited for the 6 acres or so that I mow there and can certainly work with some of the other things I do there like dragging downed trees to a burn pile and stacking them with the loader. There are times I would like to have the weight and greater strength of the loader of an L, but because I trailer it 30 miles, I feel the B is a good solution for me at this time.
The Kubota line is pretty confusing with what seems to be some overlap, but best to look at what you are planning to use the tractor for and then decide which is the best fit. Or buy one of each.