In my point of view, I think as per contests, codeforces is better, they have a lot more contests. Good blogs from top coders like Gennady, Petr, Egor, rng58. Along with that codeforces have a bigger audience., Most of the top programmers frequently code on codeforces like Gennady, Petr, Egor, rng58. As far as I can see on codechef Gennady, Petr participated only 1-2 contests in a year on codechef.
A competition is as good as it’s competitors, clearly, codeforces have more from top-tier programmers.
But codechef is better in its own way like long contests give you enough time to read concepts and work over it.
it’s a way how you want to code if you want to code more frequent in a more competitive environment codeforces is the better option. If you want to code less and learn to debug and all then codechef is better.
One more thing to notice codeforces have a super fast rating system, while codechef takes 10s of days. They never reveal all test cases so that you can code accurately in the first try(Gennady’s Philosophy write correct code so you don’t have to debug.).