In no particular order;
1. Cassie; everyone is just hating on her for not having a mental breakdown after the war and moving on with her life. And probably having a boyfriend that is not Jake.
2. Ax; he often gets the short end of the stick - he is stranded on an alien planet at an age equivalent to the rest of the Animorphs, his big brother is dead, he is the sole survivor of his domeship for most of the series and all the times he has a chance to go home but doesn't. That is rather heartbreaking. Also, he tortures Chapman. There is something to be said when an adolescent tortures another sentient being. Finally, he prevents WWIII by threatening Visser Two to drop a nuclear bomb on the main yeerk pool, and with it, his friends home and family in addition to his own home and likely victory. No matter how many medals and titles and honors he will get, that stuff will stay with you. Until you've lost your soul.
3. Ellimist; it's like Tobias except an infinite times worse. 'Nuff said.
That truly all at the time being. I'll have my other two later