Depends on the airline.

On LH upper deck is first so yes they leave first. On most airlines upper deck is business, but another business zone on lower deck - these leave at same time but I can get out quicker from the appropriate seat lower deck (aisle on either bulkhead or last row depending on if door 1L or 2L likely to be used). Some airlines, eg SQ, will hold economy pax back so all business class (upper and lower deck) leaves first. Other airlines, eg UA, do not bother and can take a while to get out from upper deck.

Best seats on upper deck are the exit row, but note the windows are not as good here as other rows.