SkimLinks is probably best for bloggers who want to write content around the affiliate link rather than add affiliate links to existing products. SkimLinks offers a lot of tools to compare commission rates and offers in order to customize your content to optimize your income. Once nice aspect of SkimLinks is that it offers lots of products for non-US creators, including popular UK brands like John Lewis and Tesco.
The online lead generation is a multi-billion dollar industry. Done right it can be far more profitable than many imagine. Everyone that I know that is in the business and knows what they are doing, for the most part, does 6-7 figures. While that's a huge range, much comes to one's ability to scale and effectively build / manage the infrastructure needed to scale.