Back to the wall booth on the side. Sometimes their busy and have no booths open in which case I at least sit facing the entrance. Situational awareness is everything in public and very easy to make a constant habit without being obsessive. I believe these types of tragedies will only increase in the future with as nutty as people are lately, so it's only good sense to pay attention when in public.
"Always place your clothes and weapons where you can find them in the dark"
"Understand that the enemy is not the enemy in his own eyes ;this may offer you an opportunity to make him your friend. If not, you can kill him without hate, and quickly."