Google has mixed its search ads between and throughout the organic (free) search results starting sometime mid-last year. Google calls it dynamic ad placement, and it is an ongoing tests. In fact, Google had to change its definition of top ads to make way for this historically very unGoogle-like move.
Personally I just use an ad blocker
Why not use another search engine, and still use an adblocker?
Because they are all worse than google in many areas, especially for local results