It depends on the niche and target audience , untidy ( non wrapped ) can be more successful because it stands out, however you also then run the risk of people seeing an advert as soon as they get on the site and leaving pretty soonish.

Personally i always stick to wrapping the ads with text, i find it looks tidier and also gives a little more relevance to the ads ( although thats just an opinion )

You know the answer George, test.

Google would rather you do the second one and
so would I.

Paul