This.  I think people assume he’s weak because they compare him to Mikasa and Eren.  Eren, who is fueled by rage, and Mikasa who wants to keep Eren safe.  But if anything, Armin is the bravest and most level headed of them all.  He’s realistic in the fact that he’s scared.  Who the hell wouldn’t be scared?  He also stops and thinks, and approaches things carefully, because if you don’t approach something cautiously there’s a chance that it can get screwed up again (the whole “let’s rush after the titans” tactic doesn’t work guys, so stop and think).  People seem to forget that (and this is from episodes 1-14 I’m not completely caught up):

1.  He’s the one who watched Eren get eaten.  Yes Mikasa’s back story is terrible and her closeness to Eren is understandable, but don’t forget, Armin and Eren are friends too.  And he had to watch this, and deal with it, and Mikasa was ready to give up, not Armin.  I’m not saying that Mikasa being that distraught over Eren doesn’t make sense, it does make sense, but Armin could’ve also been that distraught but instead he kept going (and lets not forget that at some point Mikasa realizes that she needs to live on, too).  Eren is a good friend to Armin, always there when people pick on him, but most importantly, he actually listened to him talking about the outside world (where Armin says his parents went) and instead of thinking he’s crazy, he was excited!  That has to mean a lot to Armin.  Everyone else thinks he’s crazy and beats him up, but not Eren. 

2.  He’s the one who suggested that they lead the titan to the main building where everyone is because the titan was fighting other titans, this was BEFORE the big reveal that it was Eren.  He noticed the titan fighting other titans and instead of running away he decides, “Hey, let’s use this to our advantage.”  And it worked.

3.  He’s the one who came up with the strategy on using the guns against the titans inside the building then the best people would sneak up and take them out.  It worked.

4.  He’s the one who stood up to the army to protect Eren when they didn’t trust him after finding out he was a titan, he stood there and defended him.  It worked.

5.  Eren and Mikasa DO NOT SEE HIM AS WEAK!  Eren relies on him, flat out saying, “If you think talking to them will work then I’ll let you do it.”  Eren knows how smart Armin is, and fully believes in him.  The series doesn’t depict him as being weak, but smart, and extremely useful.  ARMIN SEES HIMSELF AS WEAK, then realizes that he’s the ONLY ONE WHO DOES.  Connie trusted him with the plan to lead the titan to the others.  Eren and Mikasa trusted him to talk to the army.  The elite army trusted him with the plan to move the rock.  He’s not weak to the team, and they all see it.

6.  He’s the one who came up with the plan to move the rock.  This is a huge thing.  Fighting the titans and protecting humanity is important, but eventually humanity is going to have to take back what was lost.  If they get deeper into the walls, there will be no room, and they’ll end up doing what they did before: sending people out on “missions,” which was just a way to clear space, as cruel as that sounds, but it’s true.  And Armin knows this, because he lost someone important when they did that.  So they NEED to take back the things they lost, and because of him, they’ve started to.  You need to fight for survival, but that means they need to get back more land so more people can live, and not run out of food or living space.  No one thought of this but Armin.  Everyone’s focused on fighting the titans to win, they’re focused on the bigger picture.  Meanwhile Armin is like, “We need to take back this wall.”  Because if they don’t, all those people from that area who moved in to the next area (which is smaller) is going to be screwed.