In my experience it's also one of the most complicated. Maybe it was just our specific use case but my experience with AdWords was 2 months of tweaking keywords and consulting with one of their free specialists. $40/day. After about $1000 we were seeing an average of $13 per conversion, and stopped. Facebook ads were setup in 5min, nothing special, same area targeting, same messaging and graphics: $2.50 per conversion.