I would go with the TDI because I just recently bought one of the original 200 made. Just getting comfortable with this machine and learning its strengths and weaknesses. Maybe the best all around detector ever made. GPX is just more than I can see paying for a machine right now since I do not nugget hunt yet. Hoping to try that in the future. ATX I am waiting for the initial sales hype to die down and see how it holds up in real world tests by real people. Strengths, weaknesses, and dependability. I now own nine detectors (crazy even by my way of thinking ). To buy another I will have to make myself sell a couple. Each has it's own strengths and weaknesses. Each has a purpose that they are ideally suited. I may have to admit here that I have an addiction to this sport. Just do not ask me how many coils I own. Now those I could see owning a few more of....LOL!