Easy, just make the ads the same. Change only your keywords. Now you can compare only 1 variable.
Totally agree with this, you will find it easier either creating 1 ad and seeing how this does, or creating 2 ads, and split testing them, after so many clicks change the lowest performing ad for a new one, and so on. Although going past which has the highest CTR to find out which one actually provides the CONVERSIONS is the next stage!!
Testing is a constant process to achieve the best figures.