[nialo]

But, is number of lines a particularly good size measurement?

Is there evidence one way or the other on whether it's better to measure size with, say, number of lines, number of tokens, or number of nodes in a parse tree? or something else?

[dang]

My understanding of the literature is that no one has found a better way to measure program complexity than lines of code. In particular, the fancier metrics (cyclometric complexity and so on) don't add any value over simple LoC.

We've debated the merits of counting tokens before, but I don't recall anyone mentioning a study about it. In real programs—i.e. when you're dealing with idiomatic code as opposed to something designed to game a metric—I doubt that LoC, lexical length, and number of tokens differ much.