When it comes to SEO, there are two important factors. Content and links. You have to have great content, ideally an article with more length works better over the long term than one that is short. And then you want to have more high authority backlinks than your competition, if you want to outrank them.
That’s basically it.
The problem is that most marketers sacrifice on the content side. When, really, you need to put more effort into creating or outsourcing very high quality articles…because you can always buy more links. But you don’t want to send a ton of backlinks to crappy content.
So, if you are building authority niche affiliate websites and are doing SEO to help get them ranked to get siphon as much free organic traffic to your content, I would highly recommend using BKA Content.
They are certainly not the cheapest, but when you are looking for the highest quality content, that is who I would choose. If you’re just building sites to monetize with things like Amazon Associates or Google AdSense, then you can afford lower quality content. And for that you can definitely go with more cost effective writers at places like iWriter, MorningArticles, and Fiverr.
On the flipside, when you do get your content written, whoever you decide to go with to outsource, for some really simple services for getting high quality and large amounts of backlinks to your sites, check out these resources: The Hoth, Link Emperor, and Blackhatlinks.