Two things, first what kind of country do you hunt? If you hunt heavy cover the shorter the barrel the better. My .375 Ultra has a 20" barrel and I'm not overly concerned about the muzzle blast. This thing gobbles up to 100 grs of powder per cartridge, and most medium bores don't produce the high pitched crack common to high velocity small bores.
If hunting in heavy cover is not a concern, then balance and handling is. If the barrel contour is light, the barrel must be longer if you want a slightly muzzle heavy balance as preferred by many. This should be combined to what is most pleasing to your eye. Some folks like long pipes on their rifles others do not.