>Which theory about aliens is the most likely?

The theory where there's nothing that needs to be explained, because statistically speaking we haven't been listening for any length of time, and haven't been anywhere.

Asking which exotic theory is most likely is like growing up on a remote homestead somewhere, where you've never been anywhere else and never seen anyone else, and speculating about what apocalyptic scenario killed everyone and destroyed everything.

It's jumping to a conclusion. Let's try leaving the homestead and spending some time somewhere, before we conclude that there's no one out there.

(Technically I guess that's a form of Rare Earth, where "rare" is defined uselessly as "less than ubiquitous.")