Well, here is my 2 cents, since you asked.....
First off, I would not bother with the full size Glock in 9mm (Although the G17 is a damn fine gun). If you are looking for a full size Glock, get the .45
In my opinion, the full size Glock is not very concealable and because of this fact, my G17 has been designated to "night stand only" work (and for that role, I would much prefer it to be in .45). The compact and subcompact Glocks are much more versatile, and make for more practical concealed carry guns. So if you have a CWP, or ever think you might want to get one, then I would think long and hard about getting the subcompact - The G26 is a great carry gun, and 10+1 rounds of 9mm is more then enough firepower for concealed carry. They are just as accurate and shootable as the big boys, and you can get a finger extension for the mag if your hands are too big.
I would also recommend getting one of the uber-high capacity mags for which ever Glock you choose. My G17 is ready to engage the bad guys with a 33rd mag - and you can also get them for the .40 or.45 Glocks. It is also important to note that all of the compact and sub compact Glocks will take their larger counter parts mags as well (so I can even use the 33 rd mag or the 17 rd mag in my sub compact G26

. Oh, and they are fun as hell to rip through at the range!
Lastly.... I would not rule out buying a used Glock. I bought my G17 used from a gun store for about $250 a few years back.... It had a great deal of finish that had been worn away on the slide, but I sent it back to the factory and had it refinished for about $40. Now it looks as good as a new Glock and it has always run like a clock. So my point here is that most of the used Glocks out there are pretty much as mechanically perfect as a new one, and if you look hard enough I know that you can find them for a much lower price (probably around $350-$400).