The four ways of winning:
1. Soldier
At the end of the map, you will find an evil graveyard. It will be overrun of zombies and it will take an big effort to clear it. Then, when you have reclaimed it, you will have to use 15 soldiers to destroy it in 10 days. Then zombie hordes will attack you every second day so be prepared. You are having a loss of 15 soldiers and defending against big hordes. In my opinion, the second to hardest way.
2. Leader
At the end of the map, you will find an city hall. It will be overrun of zombies aswell. After it's cleared, you will need 5 leaders and 10 days to create an goverment.In my opinion: The easiest way.
3. Labratory
After everything else is researched, a cure zombism research will be unlocked. It will take 5 scientists, 18 days(if i remember correctly) and 3 labratories. In my opinion, the second easiest way.
4. Bulider
Capture every square at the map, the hardest way.