I prefer adnetworks because it provides a reliable steady stream of income while affiliates pay more, you have to make a sale to be paid.
imo it depends of type of traffic your site gets. for example, if you have arcade site, then I'd install adsense on it, because most of traffic are kids which won't order anything online (excepting some cpa offers for zips/emails). but if you have site about viagra then i'd install some affiliate program
Adnetworks usually. It depends on the type of traffic. If you can find a decent affiliate program with the same kind of content to your site then do it.
Adsense is safe and on time but not get much wihtout high traffic, Affiliate Marketing is paying much better but not reliable....
Affiliate marketing for me... because i'm more familiar with it... as for the adnetworks, i'm starting to study it first...
I think you need some of each. I am trying some pay per leads from CJ on my new arcade site to see how that works out, but I also have some affiliate links and adsense on there too.