A direct response advertiser is primarily interested in generating conversions from a display campaign. To get the best return on investment, this advertiser should use:
- Ad Scheduling
- cost-per-day (CPD)
- Target CPA Bidding
- cost-per-thousand impressions (CPM) bidding
Explanation: An automated bid strategy that sets bids to help get as many conversions as possible at the target cost-per-acquisition (CPA) you set.
Note: Conversion Optimizer is now Target CPA bidding
Read more here: https://support.google.com/adwords/answer/2390684?hl=en