Affiliate marketing and niche marketing are the same, and yet different, depending on your approach.
If you are selling your own product, that tends to be niche marketing, if you are selling another persons product in exchange for a commission, then that is affiliate marketing. At the moment both of these areas are hotly contested, with people jockeying for position to find the next great untapped niche.
I reckon the money will always be good with pharmaceuticals, because if you have a blog with a colonix review on it, you will probably draw a lot of traffic, so best you throw in some contextual advertising, as well as affiliate links…
