So let me get this straight - you want a gun to add to your collection, you're not trying to get any specific utility out of it, you just want a new gun to shoot? Not that there's anything wrong with that, it's just a very broad question. Guns are very individualized - some people will love a certain platform, other people will hate it. Case in point, you've asked a dozen people here and gotten a dozen very different answers. If you just pick the most popular gun everything things deserves to be in your collection, you'll have another line item on your list but there's no telling if you'll have a gun you actually like.
I think you just need to find a gun you enjoy shooting. Get out to the range and shoot a bunch of different guns until you find something you like. Do you have a range that rents guns nearby? What about friends who'll let you shoot their guns. Try and AR, try an AK, try a 1911, try a bolt rifle, try some milsurps. You'll be able to figure out which one pushes your buttons.
But if I can give you one piece of advice, it's, "Don't be a cheapskate." If you decide you like a gun that's generally out of your price range (the 1911, for instance) and you go out and buy a $399 piece of crap just to have one, you're never going to be happy with it. If the next gun for you is out of your price range, wait and save your money. It's worth it.
(on that note, a decent used Colt or S&W 1911 can be had for around $650 - save a few buck more, you know you want it)