The main concern with Craigslist bikes is that they often need a lot of maintenance. If you can do it yourself it doesn't cost much, but if you have to pay a shop to do a lot of repairs it can get expensive. That last Fuji bike looks nice if it really doesn't need any repairs. The front suspensions on the other two aren't very helpful, and are just one more place something can go wrong. Just be careful that you don't buy a bike now because it's $50 cheaper, and then find out it costs more money (and headaches) to keep running in the future!