As a semi-backup detector, I use a full setup XP Deus 1 metal detector. Not just because it’s one of the most technically advanced and adaptable detectors on the market, but it’s also the lightest of all the top-end detectors too. Perfect for using all day without tiring yourself out (and also easy on my shoulder’s rotator cuff injury too 😀 )
Currently, I use a 9″ X35 coil. It covers all the “sensible” frequencies and I’ve had some very good results with it. I formerly had another Deus 1 with the 9″ HF coil as a backup machine but passed that on to another detectorist.