I own a sw99 in 40 cal and have shot an oss in 9mm. They are both great guns. But personally i prefer the sw due to the fact that i love the grip on this pistol, and some people dont like it, but i really like the AS trigger on the sw99. It feels alittle mushy in SA action, but once you figure out the pull it great. I shot alot more accuratly with the sw99 even though it was a 40. That being said. Im actually looking to get a 9mm for cheap as a back up gun and im looking into either the OSS or the PT99. But im not sure if there are 2 versions of the pt, ive seen one that looks similar to a 1911, not the one i like.
Honestly if you can try rent or shoot these at a range.