You can complete Loop 1 easily with any members (heroes) in your party, however, a more balanced party would make your life much more easier. Depending on maps, a balanced party should consist of one spearman, 1 mage, and 1 sabre (or hammer). In maps where there are aerial enemies, you should include 1 or 2 archers as well.
Here’s my typical party composition:
1. Loop 1
Xiahou Dun (main damage dealer), Cao Cao (supporting fire + boosting), Guo Jia (mage), Xiahou Yuan (Archer), and Zhang He (Archer).
2. Loop 2
In Loop 2 the party composition is a lot more diverse, and it differs from map to map. Play a couple of rounds in easy mode, and get familiar with the various waves before deciding on who to use for the insane level. In some maps, life is easier to have 3 spear wielding heroes, while on others, the party might consist of 3 archers and 2 mages.
I do not have a fixed start up for Loop 2, and below is a list of heroes that I have used.
Xiahou Dun, Zhang Liao, Yue Jin, Li Dian (replaced by Cao Pi towards the end), Jia Xu, Sima Yi, Guo Jia, Xu Chu, Xiaohou Yuan, Zhang He, and Zhen Ji.
3. Endless mode
Xiahou Dun/ Zhang Liao, Guo Jia, Zhen Ji, Xiahou Yuan, and Cao Pi.