When I mess up a problem on codeforces, I immediately see the test case for which my solution fails. Since that’s not possible on codechef, it allows me to think more about where I could go wrong.
Suppose that this happens to you:
Codeforces doesn’t allow you to see the full test case. In a case like this, there is no difference between the two sites.
And,
But I think that being able to download test cases is a nice idea.
Also, I’d like to have a ‘copy’ button which will let you copy the sample test cases.