dhearn, when you say "what is the best beach machine", that question is way to vague and "loaded". You have to be specfic on the type beach, your type goals, etc...
For example, did you mean the balls-to-the-walls absolute deepest seeking? Then you can get a nugget pulse machine, of various sorts, and GAURANTEED you "won't miss a thing". You can find birdshot and staples, pinheads, bobbypins, to insane depths. And coins to 1.5 ft. or more! And you'll be utterly content you "haven't missed a thing" and can look smuggly at those poor souls who only have a standard coin machine, who *only* reach to 11", and miss dangly gold tinsel thin chains, and earing studs, etc...
However, you might find yourself "hating life" by having no disc, and digging nails or bobby pins at 1 ft! I mean, pity you when you're trying to work the beach after a storm, where targets are everywhere, and depth becomes a non-issue, and speed becomes the name of the game. Your pulse machine may make you the laughing stock on days like that, where you'll suffer 10 bent nails for any conductor you dig
Or as one person humorously put it: The good news on the beach pulse, is that it's SO sensitive, that you can pick up bobby pins at 1 ft deep! And you know what the bad news is? That the beach pulse is SO sensitive, that you can pick up bobby pins at 1 ft. deep!
So it just depends on what you want, your patience and tolerance, the type beach you're hunting, mineralization, etc....