I believe it will depend on your intended use. A 3 1/2" or 4" will be easier to carry, but a 6" (due to longer sight radius) may be more accurate for you to shoot. Also, the longer barrel will develop a little higher muzzle velocity, which would be to your advantage if you intend to use for long range shooting or hunting. Also the longer barrel seems to adapt better to scope of red dot sights for longer range shooting or hunting.

For general purpose plinking or home defense the shorter barrel will probably be more convenient for you. Would suggest you go to a store that has some in stock, and see which one fits you best for your intended purposes.

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H Richard
SWCA1967 SWHF244