So which one makes more sense on a troubadour and why? You can buff ancient memory further with the +50% healing buff; but i think if you activate the troubadour modal you get less healing? but more damage shield? 

Ancient memory or Vampyric song if you don't use Brisk. If you use Brisk - Courage thick as Steel is better, 10 pt shield each 3 seconds is three times more effective and isn't negated by constitution debuffs (-% to healing).