I recently picked up another Schonstedt, the GA-72CD. That makes 3 now.
I have:
1) my old GA-52Cx, so used that the cover is loose and you have a hard time seeing any paint left. I've lost about 5 of these over the years, from "borrowing" by others. It's hard to fault this old bugger except for the hand fatigue from lack of a decent handle.
2) the new to me GA-72CD (the long one with the handle and the ribbed shaft). I haven't used this one a lot so far, but it has switch positions instead of an infinitely variable pot like the old one has. I do like the grip for hand fatigue though. It seems a bit lighter.
3) the GA-92XTd (the retractable pistol grip model). This goes nicely in a holster since I carry a shovel and robotic pole already.
I do work in both urban (chain link) and rural (buried barbed wire) environments.
Which of these do you guys prefer and why? Which are more sensitive and do a better job of detecting irons in challenging environments?
My fav is the good ol' 52c.

I couldn't count how many of these I've purchased over the years. All but one lived a good long life and either got traded in or retired (cannibalized for parts).
The one casualty was my fault..it was leaning up against the tail-gate and I backed up a few feet...the end was swift.
I have used several other kinds, but these seem to do the job just fine. After years of use you kind of get a "sixth sense" using them around fences and what-not...we call it "the force".
My only gripe is that my ears are gone. Next to traffic I'm bent over with my head crammed down on the speaker...a sad sight, indeed.
I have used all the Schonstedt locaters at some time over the years. I got tried of the cover on my 52c coming loose and was never comfortable to hold. I switched to a Dunham & Morrow DML2000 and love it. I it is light weight, easy to hold and is $200 cheaper than the Schonstedt. The sound and sensitivity it very similar to the 52c, so not much to get use to. Just my 0.04' worth.

I agree, they are the only one I know that has a jack for a headphone.
0.02
I agree the 52C. I've had my 52C since the mid 1980's, I've replaced the variable pot a few time due to wearing out the switch. The foam in the case has long ago turned to dust. I wish everything lasted as long and worked as well as a Schonstedt.