I've never been super happy with Ardour. Using the in-distro build used to crash some years back, and more recently wasn't able to get it using some audio interface. And I'm not in love with the interface. But my impression from what I've read is that it's more on-par with other DAWs than Audacity is, does stuff like non-destructive editing. Audacity is, as I understand it, considered something of a lightweight application. If someone is looking for something more on par with some other DAW that they're familiar with, Ardour might be preferable.