I've flown the 1900D, J31 and the Metro 3/23 and the only one that could carry 19 pax and bags all the time with no limitations was the 1900D. The M23 came close, but you needed water meth once it got hot and high. The M3 could really only carry 16 and like the the M23 you always needed water meth. The reliability of the M23 was better than the M3, but it was never anything like the B1900D.
The J31 while it had a large cabin and a well laid out cockpit like the M3 it really was only a 15-16 seat aircraft. It was a pain to load the bags and like British cars, working on it was a nightmare.
So while the 1900D is the most expensive of the 19 seat aircraft, it is also the only one that is truly a 19 seat aircraft (in all conditions) and you can't beat it's reliability. Which if you want return customers you need an aircraft that reliable and can operate without any limitations.