This is a topic that I believe should spark some debate here at RAF. I mean, we all have our favourite Animorphs characters, and therefore we have different views and opinions on which character sacraficed the most for the Yeerk-Andalite war. Whether the character is one of the main Animorphs, or an Andalite, or a member of the Chee, vote which main character you feel gave up the most for the war by the end of the series, and then state why you believe that character deserves this title.
Let me start by providing a brief summary of all that our beloved characters sacraficed for the Yeerk War:
First, there's Jake: leader of the Animorphs and responsible for the deaths of 17,000 hostless Yeerks. By the end of the series, Jake lost both parents to the Yeerks, was forced to kill his own brother--and, by doing this, condemming his own cousin to death-- and was infested by his brother's first Yeerk. To add to all that, Jake became the personal play-thing of Crayaks; having experienced countless nightmares of the "big red eye" following the events of the Capture. But, perhaps most important of all, the psychological damages that came from making life-and-death decisions for his teammates, as well as innocent bystanders and hosts alike, is more than enough for Jake to earn this title.
Next, we have Rachel: Jake's reckless and headstrong cousin, and love interest for Tobias. Unlike Jake, Rachel's family was completely cut off from the Yeerk war up until the events of the Diversion. She had a perfectly ordinary life prior to the war, and managed to learn to cope with her double life after meeting Elfangor. Despite her parents divorce (which was unrelated to the Yeerk war) Rachel has sacraficed little in the family department. And while she did have to endure that inner self-conflict of good vs evil, being tempted by Crayak and the "dark side", etc., this is not, in my personal opinion enough to give Rachel the title of the Animorph who sacraficed the most for the war effort. However, that does not mean she wasn't brave, dedicated, and significant.
Thirdly, we have Tobias:the universes personal whipping boy. His father was taken from him; his mother was unfit to take care of him, thus leaving him in the hands of two uncaring relatives; and he grew up as an unloved, socially awkward and constantly bullied. We also have to add the whole "getting-turned-into-a-bird" situation from the invasion onwards, as well as his conflict of "am-I-a-bird-or-human-or-Andalite?" (though that's a separate debate, in my opinion) to the list of why Tobias deserves this slot. But, most importantly, Tobias loses Rachel by the end of the series. The one other human being who actually cared about him was taken away from him, thus forcing him into obscurity and depression. Also, despite having reunited with his mother after more than a decade, he is still alone, because the woman can't even remember him, and seems to care more for her dog than her own son.
Then there's Cassie: tree-hugging moralist of the group, and famous for being the only Animorph to live by the end of the series. Jake was depressed up until the "lets-save-Ax-and-get-ourselves-killed" mission; Tobias was pretty much 100% bird after Rachel died; and Marco tried to mask the pain of his involvement in the war by buying a lot of stuff. And what happens to Cassie? She keeps her parents--who were only involved in the war from book 49 onwards-- and seems to have a respected position in society. She has a boyfriend, and is seemingly okay with everything that happened in the war. Sure, in the beginning of the series, we see a little depth in her character--most specifically in the Departure, where she starts to wonder if her own actions aren't the least bit hipocritical-- but that sort of simmers down once the ghost writers take over. I think we can say Cassie gave the least to the war effort, aside from some psychological trauma.
Marco: pragmatic, realistic funnyman. The kid had it pretty rough after his mother "died"--what with his father slinking into a depression that is only rivaled by Jake's post-war. From the moment his mother dissapeared, Marco had to take care of himself, as well as his father. And if joining a resistance against brain stealing aliens wasn't enough to send him off the deep end, discovering that his mother was the leader of the invasion of Earth would have done it. And he was constantly debating upon the fate of his controller-mother: should I kill her and move on? But, ultimately, by the end of the series, Marco makes it our more or less alright.
Ax: our resident Andalite, and prodigal younger sibiling. He was forever living in the shadow of his older brother, especially after his death. Ax was also tortured with self-conflict: that is, avenging his brother's death by killing Visser Three. And then there's the whole "isolated-alien-living-trillions-of-lightyears-away-from-home" bit that we get from Ax throughout the entire series. But, when you really think about it, up until he gets assimilated by the one, Ax more or less makes it out alright. His parents remain uninfested, he managed to adjust to life on Earth--albiet, still lonely-- and he earned himself a respected position in the military. Sure, his brother was murdered, but Ax was able to cope with that thanks to his friends.
David: traitor to the Animorphs. I doubt anyone will actually give a damn about David, and I don't expect a lot of people to sympathize and vote for him. But you have to see it from David's POV--the kid had everything taken away from him. Both parents were infested by Yeerks; he witnessed Visser Three morphing and destroying half his home; he was left no other option but to live in a stranger's barn and join a group of soldiers that would rather not have him around to begin with. When you really think about it, David was only an Animorph for a week--that's seven or more days that he was allowed for everything to sink in. And obviously David was psychologically unbalanced to begin with. Now, that's not to say that David wasn't wrong in what he did; he was. But you can't just write him off as a horrible human being.
Those are the main choices. I added Erek, James and Elfangor as after thoughts. If anyone else wants to add something--like a character that I forgot-- then feel free to tell me.