The most important element of a banner

Hi guys!

So after testing some banners, I have found a specific layout and angle that works well.

Which of the following elements should I test afterwards?

In other words, which elements are more influential to the CTR/CR of a banner based on your experiences?

1. CTA color
2. CTA text
3. Border
4. Image
5. Other (please specify)

Any input will be much appreciated!