Hanji is my favorite,her introduction was funny as hell,I like how she analyzes situation and acts, followed by Armin,Eren and Annie.As a hero,Eren continues to get better,I like how he trusts his teammates and some of his quotes when he explodes are just awesome.
Reiner,Jean and Rivaille are the following.Reiner especially,he really is a true soldier.
My favorite is Rivaille. I wasn't expecting so many other people to choose him as their favorite lol. He is just a freaking beast. Pretty much untouchable in battle. Aside from him, I also really like Mikasa, Annie, and Reiner. I wont even mention liking Sasha because that should be a given for everyone. She is hilarious.
Jean. Because he's just so....real.
Mikasa and Sasha aside, I would say Jean.
He is, as Marco puts it, at the lower end of the chain of command and is able to understand and speak out for them. And I love his honesty.
Rivaille is also very admirable, for his strong resolve in his duty and as a vice-commander.
Mikasa is very cool and strong, and Sasha is the one and only potato girl.
To be honest, a lot of characters are very admirable, even the relatively more cowardly ones. The admirable quality doesn't have to come from their 24/7 unwavering resolution, it can simply be a single second of courage, that which is enough to change their intentions. Most, if not all, characters are fighting for something, whether they realise or not, whether that 'something' seems important to other people or not. Definitely not an easy life to be in any of their shoes, but they still fight it out with or without the epicness, and go out with or without a bang.
As an aside, Jean is somewhat an embodiment of at least half the guys out there. He really reminds you what the reality is, especially the reality within the lower class soldiers.
He was portrayed as a badass fighter who appears to don't give a shit about things:
Only to show shortly after that he actually is a really nice guy:
Such characters usually are liked by many. Not saying that's anything bad, I like Rivaille too and I think Isayama did a splendid job of portraying his personality in a few panels