Which tool chest should I buy?

The current Craftsman and Kobalt boxes are all made in China. From what I have seen, the Harbor Freight boxes are just as well made, if not better made, than the current batch of Craftsman and Kobalt options. Same for Husky. Costco has some nice stainless steel tool boxes, although it looks like they're a little more expensive than your current selections.

For the new toolboxes my suggestion would be to look at them in person, check the drawer slides, layout etc and think about what you like best. Look at the weight ratings for the drawers, the harbor freight boxes are better than a lot of the Craftsman boxes on that accord. Heck the Harbor Freight boxes have better weight capacities than some of the new Snap-On boxes (which are not all made in the US anymore).

As for the used Snap-on box, it looks pretty rough. I have a bunch of tool boxes, a newer stainless steel Craftsman box from about 10 years ago and then some 70's era Snap on, Craftsman and Matco tool boxes of similar vintage. Of those the Snap on and Matco boxes have the better drawer slides, the Craftsman boxes from the seventies (ish) have drawer slides I'm not a fan of, they just feel cheap. The drawer slides on the Snap-On and Matco boxes can be repaired, but the only place to really get those parts is from a Snap-On truck. And despite the lifetime warranty the older slides are a different design than anything that has been used for the last couple decades, so, you may not be able to get parts for a specific slide type. They can be repaired if they're not too hammered, I pulled apart the slides on the Matco box, cleaned and lubricated them and they work a lot better than before. But they're still not all perfect. If you really want to restore an older tool box you can check out The Garage Journal, lots of info there about restoring older tool boxes. It can be pretty involved, you could easily end up spending a lot of time restoring a tool box that you could have spent working on your car.

So, my advice for the used tool boxes is to make sure you check them out in person and test all the drawers. If the slides are a little sticky they can be cleaned and lubricated. But if they're jammed or the drawers are bent up it can be a lot more time consuming to repair them. And usually used Snap-On boxes cost a fortune, people always want a mint for them even if they're beat to hell. So even though I like to buy the older, better made tools and stuff I don't always recommend buying used tool boxes. I've done it, but like I said I'd be picky about checking them out. If they're beat to hell you'd be better off with a newer one from Harbor Freight. Your time it worth something too, and you could easily spend days just cleaning up an old box only to find it had a drawer or two that will never be quite right.