ESPN is the worst site I've ever used. It's clunky, non-intuitive, and often has problems with traffic overload. And that was last year when it wasn't free. Imagine what the increased traffic is going to do to that site.
Yahoo certainly is the big boy in town, it's reliable and simple, but don't discount some other sites out there (hint hint). Free leagues are to be had from smaller sites as well, with cheaper live scoring. The biggest doesn't always mean the best.