Let me say this: Garrett has excellent metal detecting technology, no one can argue about the performance of any of the AT series detectors, frankly. I think where Garrett has fallen short is on ergonomics and user interface. Here is a rundown of some other brands and how I think they compare from a US user's perspective.
In that regard, I think First Texas does a great job without sacrificing performance that is on par or exceeds the AT series in some respects.. Their F75/T2 interface and shaft/stem balance are excellent, however, they apparently have no interest in making a high end submersible detector.
Minelab has perhaps the best metal detecting technology out there with multi-frequency and stable target ID algorithms - their user interface, however, with all the submenus and unnecessary settings. We'll see if the Equinox bucks the trend on terrible
Whites has good advanced technology machines, but again, their user interface leaves something to be desired on their high end machines. Very good mid-level machines, the MXT perhaps being the cream of the crop for a workhorse detector in its price range.
Tesoro - simplicity and no frills performance at its finest.
Makro/Nokta remind me of a foreign First Texas with some innovations. Still no submersible machines though.
Deteknix/Quest - Their Quest series detectors are worth looking at. The Quest Pro may give the Equinox 600 (but not the 800) some competition.
XP Deus - just a different animal altogether. Performance is excellent. Ergonomics is great (feather weight, completely wireless). User interface could use some improvements but overall a great package. Not so great wet salt beach performance and kludgy add-ons required to make it somewhat submersible. Perhaps went too far with wireless technology (submersible challenges and coil cost) but it does have its operational advantages.
#1 In detecting technology - Minelab (CTX 3030)
#1 In Performance and Ergonomics Technology - XP (Deus)
#1 In User Interface and Performance - First Texas (F75)
#1 In Grab and Go - Tesoro
#1 Workhorse Performance and Value (Submersible)- Garrett (AT Series) [Equinox could steal the crown, we'll see]
#1 Workhorse Performance and Value (Non submersible) - Whites (MXT) and First Texas (Teknetics Patriot Series)
Up and coming detector manufacturers making a dent in the US: Makro/Nokta and Quest/Teknetix
Again - the best detector out there at the moment is the one you have swung the most with your own hands.