The first answer is to try each one full time for a week and see which one is better for your use case.
For my part, I loved the eye candy on perplexity, but I caught it mixing up answers a few times and I lost confidence.
The other part is that I felt passive in the search process, while on Kagi I am/feel empowered thanks to the advanced controls.
I'm considering them both, buy I'll only pay for one...