I can't decide, so here are my top 10, in order of appearance:
Colossus - Finally this character is utilized to good effect. I don't care what he's supposed to be like in the comics, I thought he was hilarious here.
Batman - I liked seeing how messed up Bruce was in this, and despite the ridiculousness of Clark saying Martha in that moment, I liked seeing Bruce snap out of his psychological funk, and I liked where his character ended up, the speech, etc. Affleck nailed it. Plus, the new suit, batmobile, Knightmare Batman, etc.
Superman - I don't know if it's just Cavill or just the territory they're playing in with these movies, but I find him to be a very endearing character -- the guy with the world on his shoulders who sacrifices himself to save it. Could have been done much better, but I still liked it nonetheless.
Wonder Woman - What an entrance. Shoutout to the hilariously over-the-top, yet creative and impossible to resist musical theme.
Iron Man - Nice to see more layers with this character. Downey killed it. I'd want to punch Cap in his perfect self-righteous teeth too.
(Gi)Ant-Man - Running in and around the Iron Man suit and the use of Giant Man were awesome. And I might have been the only one who found "does anyone have any orange slices" to be hilarious. So Paul Rudd.
Cyclops - I just thought it was nice to see Cyclops again and shown as the powerhouse character he is. I'm talking about scenes like Scott accidentally splitting Xavier's favourite tree. And I thought Sheriden nailed it.
Quicksilver - The actor plays it all so chill, yet I found him quite endearing in this.
Deadshot - I dug Will Smith's sarcastic pessimistic Lawton. Those few scenes where he shows off what he can really do were so awesome as well.
Doctor Strange - I never knew Strange had that much personality. The images I've seen of him from the comics never really exuded much of anything, so I was pleasantly surprised with the character and Cumberbatch's performance.