Google will be rolling out some changes to AdWords Conversion Optimizer and Enhanced CPC next month. These include new ad rotation defaults, a "rotate evenly" change, and eligibility for campaigns to switch to "Optimize For Conversions".
In a post on the Inside AdWords blog, Google product manager Wilfred Yeung writes, "Using AdWords Conversion Optimizer or Enhanced CPC can help you get more conversions at lower cost, and reduce the time required to manually optimize your bids. When using either one, changing your ad rotation from 'Optimize for clicks' to 'Optimize for conversions' increases conversions by an average of 5%. That’s because 'Optimize for conversions' shows your higher-converting ads more often."
"To help you get better performance with AdWords, we’ll be linking these options more closely together in a series of changes that we plan to roll out during the week of November 12th, 2012," adds Yeung.
When you activate Conversion Optimizer or Enhanced CPC in a campaign your ad rotation setting will change to "Optimize For Conversions" by default. Google says you're most likely to get the most conversions this way, though you can still change it if you want to.