There isn’t one. And don’t believe website builders that claim to have "great SEO".
The only thing a website builder can effect is your website's on-site, technical SEO. And on-site technical SEO is generally the same across website builders— the differences tend to be minor.
In short: the website builder you choose will only have a trivial effect on SEO.
Instead, focus your SEO strategy on creating great content and a great user experience. Google will reward that.
If you’re interested in learning more about SEO, I’d recommend reading Moz’s Beginner's Guide to SEO.