Have a 16QBH for last 2+ years. The half bath works well for traveling, and I get my stuff in the half and she gets the full bath in the rear when stopped. I can't say anything about the other since we never considered one. Less space? Don't know, haven't had the single bath unit. We are full-time for 2+ years.
In either case, do research on the Big Three mentioned above, expensive if not done already.
'16 40QBH Phaeton
'21 Sahara HA toad
'15 38RSSA Mobile Suites--traded
'05 36TK3 Mobile Suites--retired but not forgotten