I really see no difference in the handling of a 18½" to a 20/21" barrelled shotgun--for HD purposes...Getting in and out of a vehicle may pose a different situation...It will not give you any increase in velocity but will give you a slightly longer sighting plane and possibly lessened muzzle flash...
Cylinder is not a choke, it is a straight piece of pipe...choke only occurs when you begin to constrict the end of the tube --IC, SK1, SK2, LM, M, IM, LF, F, XF and/or turkey...Although they do make a cylinder screw-in tube, that's only to protect the threads from damage...
For HD my preference is for a Light Modified (LM) or Modified (M) choke just in case I have to shoot at 15 yds (the length of the house) and my coach gun is bored M/IM (Improved modified) taken down from full but both pattern on the loose side of their ratings...
For some reason, rifled slugs, usually perform better from a choked barrel then cylinder but buckshot doesn't particularly like anything more then modified before starting to make donut patterns...
There are some after market barrel makers that have short barrels with tubes for yours...check out the big name gunnies like Brownell's, Midway etc...
FYI
Choke.....% in 30" circle at 40 yds
Cylinder.....40
Skeet........45
Skeet 1.....(46.5)
Skeet 2.....(48.5)
Imp Cyl......50
Light Mod...55
Modified.....60
Imp Mod.....65
Light Full....68
Full...........70
Extra Full ...75
Super Full...80