Well, one difference between Rand Paul and Johnson would be that Paul currently holds office. In that sense, Johnson is definitely more Libertarian.
People who want Hillary to win should definitely vote Libertarian. By the way, I’m a libertarian with a small “l.” Gary Johnson is no libertarian, in my view, however much of a Libertarian he may be.
Rand Paul is a mixed bag, but some of his nuttier Libertarian tendencies have been tempered somewhat by common-sense conservatism. In Johnson's case, there is no sanity for counterweight.