First I'd nail down what you're going to be using the gun for. If it's just a range toy then you can buy virtually anything you want/can afford, if it's for defense or range toy/defense then you need to start considering finer details, if it's for concealed carry then there's a host of details to consider + legalities.
Assuming given your post that you're still in range-toy land (which is a perfectly fine and fun place to be), all I'd say is avoid anything branded Jimenez or Bryco. They're actually the same company (Bryco no longer exists), but they're the modern descendents of the saturday night special. Ultra-cheap, ultra-fail in practically every respect, sometimes ultra-catastrophic-fail.
Other than that, I'd also typically focus on a gun that has some practical utility and a good reputation, as opposed to something like a Desert Eagle, although cool, is pricey and temperamental.
As for used guns, most are fine. A well-made gun lasts a lifetime or longer, I read an article not too long ago where a columnist purchased a parts-matched (original parts) WWI era 1911 (military-issue handgun) and shot a competition with it. Wasn't as accurate as a finely tuned race gun, but it was still dead-reliable after almost a century. That said you should do your research if you're buying used. Get the prospective purchase's serial number and google it to see if there were any known problems with that batch (ie: is it being sold "used" for a reason).
If you want a good deal on a nice gun that could serve both range toy and defensive uses, I'd look for a Sig Certified pre-owned. These guns are typically ex-law enforcement that were traded into Sig and factory refurbished, and they're usually just as good as the new ones but at a substantial discount. They aren't cheap, but you probably won't ever need to replace them either. They're sold with a "Sig Certified Pre-Owned" ribbon wrapped around the grip, easy to identiy.
If you're on more of a budget I'd look at something made by Ruger. They're solid, American-made guns with excellent customer service and good reliability, and a great bargain. They typically aren't that flashy, but they're the best bang-for-the-buck gun you can buy IMO.