Assuming, since you are thinking of scoping, the gun may be used for hunting.
I like a longer barrel over a shorter barrel. Just balances out, steadies and settles in better for me. I have a 4" S&W .44 Mag that is a wonderful gun. Wouldn't wanna have to hunt with it. Have a Taurus .357 Mag with a 6" barrel that is NUTZ for accurate. Balances superbly. IMHO, the .357 Mag is on the light side to hunt with unless that's all ya got...….and even then...…. But it's great fun to shoot. Have a pair of 6" .401 Power Mags......one scoped, one not. Extremely good shooters. And have an open sighted 7 1/2" Ruger SBH .44 Mag. Probably the nicest one of the bunch as a pure hunting handgun. Maybe only the scoped .401 surpasses it.
I'd opt for a 6" over a 4" gun EVERY time.