Obi-Wan and Luke

Vader’s lost to Obi-wan multiple times, and Palpatine’s beaten the crap out of him in the comics. Before his fall, he lost to people like Dooku.

Previously, Anakin did not have a leg up on the competition.

You gotta hand it to him though, after he became Vader.

Asides from Obi-Wan and Luke, Vader had a pyrrhic victory in his duel against Ahsoka on Malachor.

While he technically won the duel with Ahsoka, he lost part of his mask and voice modifier, and then fell as the Temple imploded. Vader limped out of the Sith Temple as a result.