Currently (was) considering the same choice.
Initially, I preferred the L due to larger frame/heavier and more CID.
Upon closer inspection, I eliminated the L series because the turning brake pedals are on the same side as is the hydro pedal. This is a show stopper for me as I regularly carry the front end and steer with the brakes.
That said, if considering a gear drive L series, such is not an issue.
The B series is a more "deluxe/premium" line. The L series is the low cost leader. Not an issue to many but creature comforts are worth something.
Additional features to consider: The B series has a mid PTO, necessary for MMM or snow blower. The L series does not.
Finally, I have a B1750HST bought new in 1994. I use it with the Kubota 60' MMM to mow my lawn and with a back blade and F & R chains to plow snow on my 1/4 mile steep DW.
In the 23+ years that I have owned the
B1750, it has needed nothing. NOTHING, aside from regular lube/oil/filter changes. NOTHING. Not so much as a fuse, lamp bulb or fan belt. NOTHING.
Yes, it has always been kept inside, receives regular maintenance, and is not abused. That said, NOTHING in 23+ years is quite impressive.
SDT