I have had both and would go with the SIG P220 (aka Browning BDA .45). The P9S I had was also a .45 and the BDA in comparison was easier to shoot, super reliable, and very accurate. When I had the BDA I also owned a Colt Gold Cup and the BDA could match shot for shot with the Gold Cup!
I never felt as comfortable shooting the P9S as it seemed a little awkward in my hand (smaller size) and it was a bit of a reach to get to the trigger. Same with the slide mounted safety, though I rarely used it. The sights were okay but accuracy was just a little above average, with factory loads or handloads.
Overall I felt the P9S was an innovative design and featured some unique technology for it's time, like it's polymer trigger guard, polygonal rifling, decocker, and it's roller delayed blowback method of operation.
An interesting gun, it just wasn't a good fit for me.