The best divide is actually far less aggressive: Platforms should be split from services. Android and Chrome are IMHO the primary things Google should be forced to divest.

I am not sure you could (or even should) split Search and Ads, but there may need to be some significant rules laid down on Google's ability to tie their other products and services to search. Strict rules should be laid down on allowing ads to sell placement above trademark holders for their own trademark, as that kind of shakedown is insane.