There are several machines that have lightening fast recovery, as any # of persons will point out (F75, etc...) However, don't overlook at that "recovery speed" isn't the only aid in work in and around iron. You also have to factor in which machines do a good job at "averaging" (or "seeing through"), as well.
Some machines that might have super fast recovery, for if objects are very close to each other, may not necessarily do well if the nail is totally covering the coin. If two objects are utterly co-mingled, then "recovery time" becomes a non-issue. In that case, you have to ask yourself what machines average targets the best. Some machines simply see the object on top, the best, and fail to let the one below it bleed through, or work to bring up the average, or whatever you want to call it.