Free Adsense: ad units vs link units, which will make more money

It's a question I had wondered in the past, yet have never really gotten a clear answer to, not even when trying to Google the answer. Which is better, ad units or link units? Which will make you more money? Sure, there are multiple answers to this question depending on who you ask, and there are pros and cons to both, but nobody's given a clear answer yet, at least that I've noticed. There's only one way to get a clear answer to this question, and that's experience. Experience and experimentation (well, ok, so that's two ways. Here's candy, smartie.)
First, what are the pros and cons?

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