Atom, RSS, auto-discovery

Which, Atom or RSS, should NetNewsWire prefer when doing feed auto-discovery?

Assume that there will be a preference to let you choose which you prefer. The question is: which should be the default?

Also assume that I don’t want to put up a sheet prompting the user to choose whenever NetNewsWire finds both. That’s a bit of complexity the newsreader should take care of.

So, the question is, which? I can see good reasons for each. What do you think?