The four I owned being three prior Explorer IIs over the years and then finally finding the particular things I was looking for in a detector with the Sovereign GT.
Have used the Etrac, SE Pro, the old Excalibur 800 model with blue headphones & heavier BBS800 coil, and the newest 2012 model of Excalibur with yellow headphones and the 10" Tornado.
Both Excaliburs I have used only on land, and with the 800 model I made a few really nice finds with it. That is what first opened my eyes to giving another Minelab a shot again. I liked the long detailed audio and smooth like butter stability and extreme depth of the thing in my soils, and even with the first outing of one on the fritz I still managed some keepers with it.
Far as the Etrac goes, not my cup of tea. Prefer the non-compressed ferrous # setup of the Explorers and a few other things about them. My biggest issue with my prior 3 Explorer IIs was the stock 10" coils that didn't seem to handle my soils well, and also the lousy pin pointing.
With the advent of the SE Pro and it's much better pinpointing software, I plan to pick one up to sit along side my GT for days I want a more "digital" experience depending on which mood strikes me, but I'm throwing a 12x10 on it and selling off the Pro Coil, and the GT is the first machine I can say that is never leaving my side no matter what else I add to my line up down the road, God willing of course.
Have owned several other brands and models over about a 20 year span, "sampling the wine" so to speak, to find what I was looking for. Some lacked this, some lacked that, but in the GT I got all I was looking for in spades- extreme depth and smooth stability in my soils/sands, huge coil selection to fit given site situations, long detailed audio yet with the numerous tone alerts of a Minelab, super high resolution in the low/mid conductor range when after rings, buttons, relics, or odd old coins that read lower on the scale while avoiding common junk like tabs when I want to, etc...