The difference is the way they charge, like Pleasure Piratess said.
The advantage of the original is that it can charge while it's in its safe little case, although that might mean it takes up a little more room in your toybox, since it has the case, or that it won't fit in your charging station, if you happen to use one. Neither are particularly dire cons.
The click 'n' charge, on the other hand, can be stored in a slightly smaller space, if your overstuffed toybox looks like a jigsaw puzzle inside, and will fit on a charging station, and if you happen to have more of the toys in that line, they all use the same charger, so that's one less cord in your charging station. The con, however, is that some reviewers have found the connection a tad finicky to make, but I personally will be willing to tolerate that in exchange for those extra inches. My toybox is full!
As for function, everyone seems to say they're identical. Unless you have a really deep g-spot, you should really be happy with either choice.