Hi:
In the past I have carried both barrel lengths for a service revolver.
Depending on the holster both can be comfortable to carry. My perferred service holster was a "Jordan Style" Border patrol holster. For this style carry a four inch barrel works some what better but I did not find a six inch barrel troublesome. I used a high ride Berns-Martin front break holster also which was great drawing sitting down. If not on duty a vertical shoulder holster or high ride belt holster would work.