Escort cards should be displayed in alphabetical order by last name. That makes it easy for guests to find their card. If you were to place the cards in order by table number, guests will take forever to find their card because the only thing they know is their name. (They don’t know their table number, hence the reason for the escort card in the first place.)
So, when you have finished your seating assignments and are packing the cards for your wedding planner, help us out and make sure they are in order by last name!