Hi,
Well, I assume you are talking induction balance (what most call VLF) detectors. I could write a book on this one but will make it brief. I'll stick with current models.
You have the Garrett Stinger, Fisher Gold Bug 2, Minelab X-Terra 705 and Eureka Gold, Tesoro Lobo ST, White's GMT and MXT.
In my opinion the Stinger is long in the tooth, and the Eureka Gold overpriced. So you get down to the X-Terra 705, Tesoro Lobo, and White's MXT for mid-frequency units with good overall sensitivity and depth. All three can be used for other types of detecting. All three are good units in my opinion and more a matter of personal preference. The Fisher Gold Bug 2 and White's GMT are both high frequency sharpshooters for those wanting to hit the tiniest gold but their extreme sensitivity makes them of minimal use for other detecting tasks, although a few adventuresome people do use them for more than nugget detecting.
Steve Herschbach