OK, I'm probably going to open up a can of worms here but which do you think is best...? I've had clients budgeting 3,000 € per month on AdWords and receiving an ROI of less than 1%. For me, targeted affiliates links are a much better use of resources but the problem there is I have to find good quality websites as affiliates and then convince them I'm not spamming them. Or, is there another route for promoting a website in a highly competative market when you know that no amount of money will deliver organic position 1 in Google's results.
Affiliates if you can get them. Revenue share affiliates has got to be the lowest risk marketing strategy out there.
IMO it depends on the niche and content on the website. If you its high paying keywords AdSense maybe better, with high converting affiliate programs that match the niche it might do better.
If you have a quality product and a well optimized landing page, it probably wouldn't be that hard to find a lot of affiliates to jump on promoting it. I think it's way more cost-effective to have a few hundred people driving sales to your product vs paying for every click which might or might not end up in a sale.