It varies with keyword, though search has usually been better better and it's a good idea to bid less for content network- that's why Google added the ability to do that without starting a new campaign- before that we had to create a duplicate campaign- you can still create a duplicate campaign only slotted for content network if you want more control over the bids because otherwise you only get to control bid at the adgroup level. You should try both search and content- and note there are two types of search- google itself and its search partners.