The colors vibrate. The lines are dynamic. The poses are like from a dance.
This is gorgeous. It's hard for me to say why, but their color schemes - blue and red, black and yellow - complete each other. The way they fly speaks of joy, of trust, of fun. Optimus, who seems to be guided, is relaxed in his state, back arched back, feet a bit curved. Prowl leans down to him, bowing to him in a pose complementary to Optimus's, so he is facing him wholly. They are both inside the blue circle with their upper bodies, which I find a great touch. While you stated they are your OTP, I can see this picture between lovers as well as between friends. Both variations are unfortunately so rare in any art work, be it drawn art or fiction.
It is too stupid that I have an idea on what they're talking about to each other and it is STUPID CHEESY NONSENSE.
Prowl: Remember, use your wings like a bird, like I taught you. Optimus: Um, okay, bird. Got it. W-Whoooa. Prowl: It's alright, I got you. Optimus: This is more difficult than I imagined; no wonder Autobots don't fly. Prowl: Nonsense, we both have wings.