Johnson, by pure default. He's extremely overrated, but the others are simply nonentities.
Eh, many Libertarians including myself didn't thing he was the best L candidate but he's still miles better than Hillary/Trump.
I am a socialist, but I understand this sentiment. I intend to vote for Jill Stein in November, but I agree with Johnson on several of his social and foreign policies, and I do think the Johnson/Weld ticket is the most qualified (even compared to Clinton and Trump), as it contains two experienced former Governors. Johnson/Weld would be my second choice to Stein.