Some questions: 1) do you intend to just do the wet beach, only in the ebb & flow of the waves, or do you intend to fully submerse it? 2) do you want one that can disc. out nails, or do you intend to "dig all" including the potential for nails?
If you don't care about nails (or think you can second guess them by sounds and such), then any number of pulse machines brands and types are good.
But if you want be able to loose nails, and even foil & such (whatever you choose), then the Excaliber is a good choice. But, while it does go deep, and while it can disc, its drawbacks are that it won't work well in extremely black sand. Also it won't find teensy tinsel thin chains, or earing studs, etc.... that a pulse can find.
So while it may seem that a pulse is a no-brainer, I have seen many pulse guys get chased off junky beaches (under piers after storm erosion, for instance) because they get driven mad by endless nails, paper clips, bobby pins, etc .... But if you're working clean touristy (non-industrial history) beaches, a pulse might be the way to go.