Aww, man, I knew Firefly would look cool as hell in your art style but you went above and beyond here. Love the pose chosen, he just looks like he's planning his next bombing with that sinister intent in his eyes. If you ever want to get started on GI Joe, I'd recommend the original Marvel Comics run by Larry Hama. It's much better than you'd think a licensed comic would be. GI Joe Resolute is another great place for beginners. Thanks for taking my request all the same, man.
Outside of him, Tifa might be my favorite of the lot here. There's some major character bias for that, but I feel like you really captured her general attitude quite well here. She also just looks so dang pretty in your style. I'm not much of a RPG guy myself, but I did love FF7 a lot when I played it. The modern ports having fast forward and the ability to turn off random encounters at a whim helped a lot. You can even instantly super buff your party if you just want to experience the story or find yourself trapped in a nigh unwinnable battle like a cornered rat.
Really, I just like this piece in general. Really cool way to celebrate 555 fans.