Glocks are easy to come by. Go to any gun shop and you will find a Glock. Why not, they are reliable, cost effective, accurate, easy to learn, easy to clean. Everybody should have one.
That being said, it isn't the most pretty and because they are so plentiful it is hard to sell them second hand. I would pay 100 more for a new one. OD might be a game changer for this.
You can't go wrong with H&K. For that matter, Sig, Springfield's HD are also great handgun choices.
Either way, you can't make a bad deal, so long as you can find GAP ammo. The FN FiveSeven is awesome, but ammo limitations are something to think about.
Will be interesting to hear more input.