What would you choose between those affiliate giants?

AdSense isn't an "affiliate giant". It isn't an affiliate marketing company at all.

It's a way of selling advertising space on your web pages so that you get paid something (usually very small) when people leave your site. I prefer people to stay on my sites than leave them, because I'm an affiliate marketer.

I don't choose between the other two. I use both.

Part of the attraction of affiliate marketing is being free to present one's subscribers with a broad spread of recommendations for products at very different price-points. There's no need to limit yourself to one affiliate network.

I started off with ClickBank only, and I'm glad I did, but now I'm trying to do a little more with Amazon as well. And some others.

On the contrary. That's what some of the people who aren't too successful will tell you, but the reality, according to people who are really making a living from ClickBank, is that ClickBank has an excellent refund policy. It's the reliability and ready availability of their refund facility for 60 days that makes the sales so easy without actually incurring many refunds at all. The number of refunds you get depends on how you pre-sell the products and what representations you make about them. Products with high average refund-rates, across their range of affiliates, are swiftly removed from the Marketplace by ClickBank, and individual affiliates with high refund-rates are doing something wrong (typically they're "selling" instead of "pre-selling", which is a huge mistake). I sell a large number of ClickBank products every month, as an affiliate, and I can't remember my last refund.

I haven't done anything in the IM niche with clickbank and I haven't had any problems with refunds. I think for joe average clickbank is kind of like a book store but for your average aspiring IM'er it's more like a library. I also second Alexa's comments that the quick refund rate has it's advantages. While it is annoying no doubt for the product creators is probably better than a FTC investigation.

If your buying into any affiliate program then its well worth having a good look around various different options! Away from IM and following other niches, by doing lengthy searches I have found some very good small affiliate programs that are very solid! Keep your options open, you don't always need the giants!