I feel a lot more comfortable using Firebug. I can't think of specifics at the moment, but sometimes I'll try debugging something in Safari or Chrome and it seems like such a PITA that I launch Firefox and get whatever done quickly.
The DOM tab is a plus, for one. It's more accessible and well laid out than Chrome's equivalent. I prefer the way DOM and other JS objects are logged to the console in Firebug, too.
Firebug plug-ins like Pixel Perfect are very useful as well. I don't know whether any such tool exists for Chrome.
Overall, it doesn't matter because you have to test in both browsers, anyway. And IE, so might as well compare it to IE's Dev tools (which have improved, but still are not good compared to FF or Webkit's).
I don't think there's anything advanced in particular present in Firebug but not in Chrome that you'll be missing.