Haven't used the 250 or 350, or AT Pro, but I have an AT Gold and it is a darned good machine. Just from reading about the different features, the AT Gold in All Metal is going to beat these other machines. Not made for salt water so that is about the only thing it doesn't excel in. When in All Metal, all targets sound off but you can set the iron discrimination and check them in Iron Audio. Yes, you will hear MANY targets in All Metal. The Hi-Resolution Iron Discrimination is a very powerful tool. I found a three inch nail one time and the Iron Audio did not sound off. I was heartbroken because it had previously been so accurate. So I checked the hole again and found a coin. And if you want tiny targets you can find stuff that is hard to see even when it is in the palm of your hand. And deep, I've found coins at 12 inches in wet sand (not salt water but lots of salt fertilizers). But more realistically, 8 to 9 inches on silver dimes in DISC 1 with an accurate target ID #. The All Metal air test was 12 inches on a good-sized man's gold ring. The lower conductors really come in strong.