I'm Under Attack! security level will still allow good bots afaik.
You should use
High unless your site is actively under attack. From Understanding the Cloudflare Security Level:
Only use I’m Under Attack! mode when a website is under a DDoS attack.
I'm Under Attack requires visitors to pass an automatic JS challenge page. From Understanding Cloudflare Under Attack mode (advanced DDOS protection) :
This means some visitors won’t be able to visit your site at all while others may get tired of waiting and leave.