Lol no are you joking makes me laugh PR doesn't influence SERPS ADsense Doesn't influence SERPS Got it ?
It's better to put AdSense between the content. This way your CTR should be higher. AdSense placement doesn't influence the SERP though...
adsense may harm your serp postition. for example, say you have adsense code right below the banner/header and before your content, then you miss out on the oppportunity of H1 tag. Search engine bots sees your adsense code before your site content which is not good for your site. put some content first, at least the H1 and H2 tags, then put the adsense code.
bad ad placement influences your RLRPs (real life result positions) - you don't get money and you start selling dope (links to pass PR) and the authorities (Google) ban you.
There is no relationship between adsense ads placements and search results ranking Bad or any kind of ad placement is not going to harm or improve your search results ranking.
I believe there is no direct correlation between any type of ad placement and rankings. Your ad placements will definitely affect returning visits, CTR, and conversions.