What I am trying to say is this:
The Pilots will in MOST cases have a better picture of what is happening outside the aircraft.
In most cases the pilots will be reading a lengthy checklist before they come to the part which sez "Order Evacuation" and won't put the QRH away to look outside, Another point is that in most big jets, the pilots cannot see some of the engines from the cockpit unless they open the cockpit windows and hang outside to get a good look along the fuselage. That all takes time and of course no guarantee the pilots are all in one piece.
With some big jets having upwards of 14 cabin attendants that's a lot more fire observers than the two blokes with pilots hats up front. Every circumstance is different and so is the wind direction. The pilots have enough on their plate reading checklists and pulling levers etc. Might be better to leave which exits to the flight attendants. The lawyers who come looking for trouble will have a harder time blaming 15 FA's than the captain.