I don't know. Eyeballing it seems to be a good start.
Why do you ask? Do you think that such things are unmeasurable or there are radically different ways of measuring them or what?
I have a hard time trying to form a judgement about whether a human is more or less complex than a dinosaur via eyeballing.
Is a grasshopper more of less complex than a human?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.