I haven't try Ghostty, but what I like about kitty is that it's performant, easy to customize (often it's just one line to add and you get that new feature you want), I like their defaults for tabs, layouts. It's not overwhelming but not too minimal either. I just find it's a sweet spot. I also somehow like the personality of the maintainer which seem to have a nice vision for the project. My major gripe is that it's not available on windows, but anyways I rarely use microslop products nowadays.
AFAIK, Ghostty is as performant. At least, on macOS. I used both and didn't see much difference. Decided to go with Ghostty as it feels more native than Kitty.