It will depend upon the application, but in my opinion they are as follows:
If water hunting where you do not want buoyancy, the MX Sport's standard 10" DD or the Detech 7" DD would be my picks.
For all other applications for land-use hunting, be it for Coins & Jewelry or in out-of-the-way Relic Hunting types of sites, there are only three coils that I feel are 'functional' and those are:
► The 6½ Inch Concentric makes a great 'general purpose' search coil for better handling of trashier sites or those that have brush, rubble or other obstacles such as playground structures, etc. This same size search coil has been in White's coil line-up for over a couple of decades and has been labeled the Blue Max 600, 5.3 Black Max, 5.3 BullsEye, and 5.3 Eclipse depending up which series of detectors it was intended for. At first they used the white colored coil housing for the 600 Blue Max, or a two-tone white over blue, then they transitioned to the black housings.
All of these round search coils have a diameter measurement of 6½ Inches and all are a Concentric configuration. There have been a few of them out for evaluation for the MX Sport and MX-7 models, and I asked and was given the okay to post on the Forums that this coil will soon be in production for the MX Sport and MX-7 models. That announcement was made here http://www.findmall.com/read.php?31,2411539,2411539#msg-2411539 on December 11th.
► The 7" Double-D made for White's by Detech is also an OK search coil for those who might prefer that configuration and/or enjoy an opn-frame search coil. Like the 6½ Inch Concentric, it is also a comfortable, lighter-weight design for long-duration, fatigue-free hunts
► The 950 Concentric, 'standard' coil on the MX-7, is also lighter than the Sport's 10" DD, and is a comfortable search coil to use in more open areas with a low amount of non-concentrated trash where good-target masking is minimal and depth-of-detection can therefore be achieved. It can provide slightly more coverage on shallower targets, if desired,
Monte
