I have a Cen-Tech, a White's Bullseye II, and a Garrett.
I like the ability to switch from sound to vibrate with the White's. Practically have to touch a zincoln to get a response, better on copper pennies and quarters, about half an inch, does well on dimes and nickles.
But, The Cen-Tech has greater range, but quality poor by comparison to either of the others and it only has sound, very noisy, at least it can be heard. It will alert at around 1 1/2 - 2" on a single quarter, about 3" on several coins close together, about an inch on a copper penny, about a half inch on a zincoln. It is the least comfortable to use.
The Garrett, my latest, is easily my favorite, much better range than either of the others, and the response intensifies as it gets closer to the object, not fond of having both vibrate and sound at the same time though, will have to tape over the speaker hole with thick electricians rubber tape. Alerts at about 2-3 inches on a quarter laying flat. It is the most comfortable to handle, and I would prefer a momentary switch instead of off/on, I think. Might change my mind on that, since it sounds an alert if left on. Want to figure out a way to tether it with some device that retracts the tether, like the old key chain devices. It would be nice if they all had a recessed eye for such an attachment. Also, the Garretts does not require balancing, it's automatic.
The White's has the best LED light, followed by the Cen-Tech, trailed by the Garrett Pro. That's my 2 cents worth on the probes I have used.