I like Firebug much more than the native dev tools, I think it has a better UI/UX. They are merging now. Firebug was one of the reasons I was using Firefox so I hope they keep the best parts of the two tools.

I don't use Chrome much so I can't really tell how good it is for developers. If its dev tools are similar to the ones in Opera (same engine) they look closer to Firebug than to FF dev tools.