I just voted for 1 mainly for economic reasons, :). I'm sure that the amount of time wasted considering this question (thousands if not millions of dollars, my sources Messers I. and P. News inform me) has far outweighed the effort in just working around defining it to have one value.

The precident for this kind of agrument is that the null graph is now almost universally not considered a graph, mainly because almost no graph theorems applied to it, so it was considered a waste of time and ink, :).

We can't allow ourselves to be paralysed by choice, or we'll never get our flying cars or rocket suits! Therefore: one.