My P11 fits in my pocket and I bet it's about as accurate as the Sigma. Mine will group 25 yard 3.5" off the bench. It takes a little practice, but I can mow down 6" plates easily at 25 yards off hand and fairly rapidly with it. Since I can't IWB most days due to dress and activities, I pocket carry, so if pocket carry is your desire, the P11 is a no brainer. I do have a very nice tuckable Rosen Workman holster for it, but never use it anymore. I pocket the gun. It has been 100 percent reliable with 115 JHPs for 12 years now. Completely FLAWLESS. Now you've heard it. You might condemn it for the trigger. I like the trigger, personally, very smooth with a slight stage at the end, light compared to revolver DAs and a long throw for safe carry.
If you'll never pocket carry, I'm sure the Sigma is a good gun, though I've heard rants on the baby Sigmas of the past. I've never owned a Smith auto, though.