I'd like to buy a 40SW or a 10mm, any recommendations?

It would be hard to beat a 1911 in 10mm for accuracy and shooting enjoyment. I agree though a .357 is about the most well rounded gun out there. I have been very happy with my semi auto accuracy out of my HK and 1911 handguns. I did own a glock model 20 in 10mm which would meet your ammo capacity requirements. It was a fairly accurate gun. There are not many choices out there that can handle 15+ rounds. I think S&W has a performance center 10mm that is supposed to be pretty nice but I am not sure what the mag capacity is.