Glock all day long. You already have a 17 so the controls and operation is all the same and you can use 17 mags in a 19. Mainly the glock has an excellent reputation and a proven track record. The p99 is probably a good gun but I KNOW the G19 is. Plus the aftermarket support of the G19 is going to be much better. The only reason NOT to buy a glock is if you fall into the group of people who just hate the way it feels and you can't shoot it well, but you already have a glock so that's probably not the case for you.
I don't collect guns, I accumulate them.