I'm going to vote for "ambient superconductor" even after this. At least we know superconductors actually exist at all, and the history of the field reflects incremental progress in terms of increasing the threshold temperature for superconductivity. With "aliens" we don't have much to go on at all, aside from vague Fermi-equation'esque appeals to "There must be aliens because the universe is so big[1]" or whatever.

[1]: I actually agree that it's very likely that alien life either has existed, does exist, or will exist somewhere in the universe. My skepticism is towards the possibility of that life visiting Earth. And mostly for the exact same reason: because the universe is so damn big.