Google Adsense or Affiliate Banners? Or Both???

This really varies depending on the keyword / product and the availability of affiliate programs (plus how much they pay). For example, on Amazon you start at 4% commission but can work your way up to more % depending on your volume.

So, for a low ticket item you may not make a whole lot if you were using Amazon and don't push a ton of volume in any given month.

What you need to find out is how much the average CPC is on Adwords for your product keyword and whether or not there are a lot of ads available. Then, figure 60% (or so) of that would be your actual earnings per click. Compare this with how much you stand to make from affiliate commission and see which would be better in this case. Each case is unique.

Also remember if you are dealing with seasonal items - i.e. - X-Mas then people typically purchase other items while they are at a site like Amazon so this can increase your commission as well. Can also happen with non-seasonal items if they buy accessories and other goodies.

As for ad placement, check out the Google heatmap for good placements.

I do a lot of split testing across all ad spots to find what pays most for each area of the site. Sometimes it goes page by page and others, I implement a sitewide change for a banner spot.