Answer the OP want , Pick 1 of the 2 in the above scenario.
I will evacuate the town & charge for the city.
My answer if the scenario is not simplified to the point the OP is trying to make:
Both option seems to lure my troops away from my current position. There is no way a capable enemy will sacrifice a fortified position for an unimportant town-- Therefore, the message has to be a mean to make me move my troops.
The most likely action of the enemy is to make a sharp push at my camp while my men is away, either at the town / his city. If I lost my camp, I will lose all the supplies and even if I defended the town, I have to retreat. The worse, if my troops fight to a stalemate at the city, I will get surrounded and annihilated.
My move: I will send a message to the town to tell them to evacuate, and inform them that I am moving to strike the enemy city. The courier would of course be intentionally captured and notify the enemy that I have fallen to his trap.
Next I will move most my supplies out of my camp, keeping only 2 days of rations everyday. The supplies will be moved to another new built temporarily camp somewhere else.
Then, I will order all the non combatants to disguise as soldiers to head to the enemy city. My troops will be set into ambush position outside my camps. My camp would be guarded by decoy troops.
When the enemy strike at my camp, the decoy troops will quickly be destroyed and routed. Roughly when half of the enemy troops are inside my camp, I will set my own camp on fire and make a sharp thrust to separate troops outside and inside the camp. Surround and destroy enemy troops outside the camp.
If possible, I will order the non - combatants force sent away earlier to return to make a surround. Since they are not good at fighting, I will leave gaps in their formations so that enemy may try to route through those gaps, instead of fighting them straight up.
After the battle, I will move on to either siege the city or just by-pass it, cuz it is no longer a threat.
People I intentionally sent to the grave : 1) the decoy troops, 2) non- combatants that may get destroyed when disguised as soldiers. 3) and don't forget the courier sent to be captured.
I love all of them, but I have to send them to die because this a cruel world and that is the way to save the soldiers under my command, and those I love back at home.