In general, I'd think the latter is better, more flexible yet stable;

One obvious advantage is that root nodes seem to have a better visibility than notes. Thank you for the added remarks too, I will certainly want to take them into account should I ever start a thing like this myself. (And I have a half-hearted idea of doing so - otherwise I wouldn't have been meditating about the issue. Incidentally it's somewhat related to another topic discussed today.)