I played around with Chrome in 2008 when it first came out in beta, and I remember finding Chrome Devtools an improvement over Firebug.

By the time the Firefox 4 betas were out, it was no contest; Firebug was very crashy (which, to be fair, it's hard for an extension to support a beta browser, but Chrome's dev and beta channels always had a reasonably stable devtools thanks to it being built-in).