Neither of those parties have the potential to become a real mass party capable of challenging either the Democrats or the Republicans. Any potential mass third party would have to have a stable group of supporters that compose a non-negligible portion of the population (which rules out the upper middle class Libertarians and Greens entirely), as well as a stable base for funding and party outreach and development.
To add to what TNF said, the American system is naturally a two party one. Unless one of those parties manages to displace the GOP/Dems (extremely unlikely), they won't have any long term success.