Jim, there are just so many variables, nobody can tell you the best program for your area. The big benefit to the units, like the DFX, is the ability to adjust the unit to your area of operations. The ground filter I use, might be wrong for you. Same goes for PreAmp gain, etc. Get Jeff Foster's book "Digging Deeper With the DFX", and study it. It takes some effort, but once you understand how to adjust the DFX, it is a VERY good detector. One of the features I use all the time is running in Correlate Mode. I search a lot of old mining camps, and most of the buildings were long since burned down. That means there are iron nails everywhere. Correlate Mode does a great job of cancelling them out. I understand that mode is also great at the beach, but have no personal knowledge of that. The big thing is just learning what the various adjustments change, and the tradeoffs they cause.
Jim
Jim is giving excellent advice. That being said, I recommend Jimmy Sierra's book "Understanding White's DFX" first. It's more of a "hands on" - "this is what each setting does" kind of approach. Followed by Jeff Foster's book. "Digging Deeper With the DFX" is indispensable, but is written more from an engineering standpoint, which is much easier to understand after reading Jimmy Sierra.
Bobby S - The DFX was White's flagship for so many years, and has an amazing reputation. To me, it is incredibly easy to operate and versatile. It's a shame it's been discontinued, but that's only because certain parts have become difficult, if not impossible, to obtain. Not because another detector is so much better.