“The only thing we’re allowed to do is to believe that we won’t regret the choice we made” – Levi

*Spoilers for Season 2 ahead*

1. So in the first OP we can see the shot of Eren, Mikasa, Armin standing together. They all look at the ground (because obviously, these guys have been through a lot) but what’s interesting to note is that Armin faces away from Eren, reflecting how he often ends up alone thinking. Mikasa though turns to look up at Eren, reflecting how she always follows him
2. Then, in the Jean version of first OP that we see in OVA 2, this same shot is used and Eren is just substituted out for Jean. Mikasa though doesn’t look up in this version and her head remains downwards. The general consensus is then that Armin is looking at Jean (so effectively Armin and Mikasa swap where they’re looking). It’s also been thought that when Jean turns his head, he is turning to face Mikasa.
   Though because this is my post I am going to jump right in here and say that I actually disagree with both of these statements (I know, it’s an unpopular opinion). Sure, screenshots can make it look like Jean and Armin are facing these ways… But every time I watch this OP I always think that Jean’s turning to face another spot of the ground. And yes, as much as my little Jearmin shipper heart would love Armin to be facing Jean, Armin honestly looks like he’s facing the ground in both OPs to me. The OPs just have some different filters in certain parts such as this one and this seems to have brightened up Armin’s eyes, specifically his pupils as they look white, in Jean’s OP… but that’s it)
3. There is so much in the first OP. The chains over the walls are meant to show how the walls provide protection, but also imprison humanity. The Survey Corps are shown to have a white-washed colour scheme and have very rigid still-shots when they’re shown, while the Titans shots are very erratic and have blood splayed over the screen. Then there’s the Survey Corps literally jumping into hell when they jump off the walls into Titan territory
4. In the OP2, Annie is featured with the other minor characters. However, she’s meant to be with the Military Police and not the Survey Corps… The shot also lingers on her as she turns away from everyone else, reflecting how she betrays them
   
5. The other characters shown in this same scene follow this same sort of ‘where I look determines where my loyalties lie’ thing. Jean, Sasha and Connie are shown to stare straight ahead. Then Ymir and Krista both linger, then close their eyes and turn back to face where Jean, Sasha and Connie where. However, Bertholdt and Reiner turn to face towards where Annie is, foreshadowing their betrayal
   
6. Armin’s mind is shown exactly how to work in the second OP. As blood rains down all around him, he stands there calmly. Then over his head we see a bunch of lit candles and as he shifts his focus onto something, all are put out but one – as he has tons of ideas running through his head, but then he shifts all of his focus upon only one
   

Sources:
Mother’s Basement – https://www.youtube.com/channel/UCBs2Y3i14e1NWQxOGliatmg
(His channel is really awesome! They have the best analysis for Ops and EDs! It’s so interesting to watch!)
Me (either through elaboration or editing what I didn’t fully agree with)