Of the 3 the MXT is the easiest and fun to use. The Sovereign GT, or any of the Sovereigns have a learning curve to them, some find it easy while other find it hard to learn. The Sovereigns are slow working detectors like the Explorer is and the Sovereigns are more of a turn on a go detectors over the Explorer. I myself find the tones easier to learn and understand with the Sovereigns as the tones seem to stay longer so you know you went over a target. Bot the Sovereign and the Explorers are better in getting the deeper coins and those close to trash as they dont average the signals like the other detectors do. I tell everyone that the Sovereigns and Explorers will give you more info for you the operator to decide to dig or not while the others detectors tell you with a beep you should dig what it thinks is good.
For hunting a area I want to check out fast the MXT does a great job, but if I am going to a well worked area where coins are older and deeper I take the Sovereign or the Explorer.
The Sovereign will put all the copper, clad and silver into one tone and number on the meter while the Explorer will give a differnt tone on differnt targets, so you can tell a dime from a quarter most times.
Depth wise i seem to dig more deeper targets with the Explorer, but also dig more nails too. As far as depth both the Sovereign and the Explorer have tied on the deepest coin.
The MXT is the easiest to use, the Sovereign has a bit of a learning curve while the Explorer you can do more with, but a longer learning curve I feel and to do great with you have to know it more and know what to set and when to set it for max performance.