Your lightly used Glock 17 and MP9 are good choices.
I would recommend Ruger SR9
http://www.cheaperthandirt.com/product/52387
Basically they looked at what the Glock did well and copied it, with minor tweaks:
-significantly thinner in the grip. This is the Glock's one real flaw...the grip is too thick for most people so they shift it in their hands a very small amount throwing their aim off, and they often don't even notice. (This was also a problem with Ruger's previous semiauto series...too thick in grip)
-ads an external fire/no fire safety switch to the side. Glock has no safety switch. You don't really need one if you are really following proper gun handling, but some people like them there.
-ads a loaded chamber indicator. Glock doesn't have this. Again, you don't really need one if you are following proper gun handling which says treat all guns as if they were loaded, but some people like this feature.
Honestly, the external safety and loaded gun chamber indicators are good for novice shooters. This is the vibe I get from you so it is why I made that recommendation