It is a combination of what features [size=small]
(controls)[/size] the detector provides to get the best performance out of an optional search coil. What the particular uses for the detector and coil might be. And naturally how the detector and coil perform for the tasks you plan to use it for.
As you can see by my Signature below, I have a few favorite Tesoro models in my
Regular-Use Detector Team:
Tesoro: Vaquero, Bandido II µMAX, 'original' Bandido, Silver Sabre µMAX and Mojave
Since 1965, my preferred search coil size for most of my detecting has been in the 5" to 7" size because they fit in and around the brush, rocks, building rubble and work between dense trash better than larger-size search coils. One Tesoro brought us the thin-profile 6" Concentric coil, that has been my primary-use fixture on the far end of the rod. I keep a 6" Concentric on my Vaquero, original Bandido, Bandido II [size=small]micro[/size]MAX and Silver Sabre [size=small]micro[/size]MAX. I used to use a Tesoro-designed Super 7 Inch Troy Custom 7" Concentric coil but sold it off long ago, and I like the 6"/7" size for general duty work and thought the new Precision 7" Concentric on the Mojave would make a great coil on one of my other Tesoro's. I also considered swapping one of those thin 6" Concentrics over to the Mojave to work it n closer to metal structures and such.
So when I got the Mojave in-hand then used it enough to feel comfortable with it's design and performance and that new coil, I started doing some swapping around and comparing all of my coils and models to find a 'best fit' for how the detectors/coils worked and evaluate their in-the-field performance. The primary goal, of course, was to determine how well I liked the new 'Precision' 7" Concentric coil, then determine which of all my Tesoro's it worked well on and would most likely provide me the best complement afield.
Well, after a lot of coil swapping and hunting in both Coin Hunting urban places and a couple if old Relic Hunting type sites, I reached the conclusion that the best detector to mate the new 7" coil to was ....
the Mojave! So my Tesoro outfit has that standard 7" Concentric coil on the Mojave and all the others sport a 6" Concentric coil. I do have a white 8" Concentric on a spare lower rod to swap over on any of my 'regular' Tesoro models, and the newer 8X11 DD RSD coil for my Vaquero. All the detectors work well, the coils work well, and so far as the Mojave/7" Precision coil are concerned, they also work great and are a very welcome addition to the Tesoro model line-up.
Well, that's about all I can share with you based on results be
me,
my types of hunt sites, and
my coil preferences. You might want to do a bit of coil swapping yourself to decide what you like best.
Monte