I'm not talking about most performant. Neither HTMX nor React has a performance issue.
The issue is overhead and complexity for the developer, and maybe, server costs.
React comes out ahead in server costs, since doing work on the client is very cheap (provided there isn't a performance issue that turns users off, which there isn't).
And in terms of dev time, it depends, but you can't say "look, with HTMX you can avoid code" because you still do need to write code, but now it's in the server.
The issue is overhead and complexity for the developer, and maybe, server costs.
React comes out ahead in server costs, since doing work on the client is very cheap (provided there isn't a performance issue that turns users off, which there isn't).
And in terms of dev time, it depends, but you can't say "look, with HTMX you can avoid code" because you still do need to write code, but now it's in the server.