...
You do know why I'm asking you this question, right?
Not really.
The Weapons DO NOT MATTER
Your Allies ARE AT ANY HEATH YOU WANT.
The Situation IS A PARKING LOT. You are NOWHERE NEAR THE SAFEHOUSE. The Spitter is TO YOUR RIGHT. The Regulars are TO YOU BOTTOM LEFT. The Tank is CHARGING AT YOU FROM THE FRONT. There are NO ENVIRONMENTAL HAZARDS. There is NO COVER.
What would you do? WHO would you shoot first?
Can I retreat from the tank? Because that's my first priority. If I can, I do so while shooting the spitter; if not, tank, then reevaluate situation. Assuming, of course, that the Regulars are farish as you imply.
Assuming sufficient ammo to kill all the zombies I expect to come across.
I fail to see the connection, however. That's due to A. who can hurt me? and B. Who will kill me in one hit? No one kills in one hit, and if the Spitter and the Tank had approximately equal damage outputs I would go for whichever had less health (presumably the Spitted).