Own two of them, a friend owns the third.
What are you looking for in a gun? What is the intended purpose of this gun?
The Cougar is the heaviest of the three, being the only metal one. It handles like and feels like a Beretta 92. It has been accurate for me. Recoil is reasonable.
The Walther feels a little thick for carry, though a lot of people use it that way. It is light, and has a long double-action first trigger pull. The de-cocker is mounted on the top of the slide, and is a button instead of a switch. It is kind of funny to use, requiring you to move one of your hands.
The controls of the SigPro are located the same as a Sig Classic. I find the felt recoil to be higher on this pistol than the others.