That's a somewhat difficult choice. I'm not a big fan of 9mm or 40S&W caliber, but when it comes to pistols/revolvers I've always believed that SigSauer was one of the best for semi-autos and S&W was one of the best for revolvers. So in your case, I'd keep the SigSauer and sell the S&W. And if the Sig happens to be a 40s&w, then that would probably be another reason to keep it over the S&W 9mm. Of course, 9mm is generally easier to find ammo for being it's a more common military round. But I guess it comes down to which one you like better, feels better, shoots better, etc... FOR YOU! good luck.