And now for my totally biased opinions:
1. Hamazura Shige - I know we had accel, but to me Hamazura is probably my favorite because he seems to be the best written out of the 3, that and he isn't an all powerful esper/magician but a regular person. It's awesome to see him flip the tables on some of the people he goes up against because he literally is working from scratch.
2. Kamijou Touma - Yes, he's a flawed character (in how he's written not just in story) but hey, he was the reason I continued watching the anime seasons and went on to read the novels before I found out how good they could actually be. I guess for me, Touma is my favorite kind of action hero, strong enough to survive insanly dangerous circumstances and take care of himself but not strong enough that things go easy for him. His power is pretty interesting and I like the way the author handles it within the mythos of this universe. As far as to why I liked him in the begining, it was simple: HE HAD A DAMN SPINE! I couldn't tell you how sick I was getting of LN mcs before I watched index so seeing a character actually stand up forhimself and others was pretty cool in my eyes... even if I treated some of his more wordy endevors as an intermission to get more snacks...
3. Accelerator: He is probably the most interesting character in the series imho. I don't especially care for how OP his power makes him that he can just do the most mundane things and have it be the end of all times, but I think once he starts interacting with LO he becomes truly interesting and his development is pretty mush the best written out of the cast. It also helps that he can be pretty amusing in some of the fish out of water situations he lands himself into like
I voted for a few others but frankly I don't think I could say anything diffrent from what some other people may say, plus I mainly just wanted to talk about my general thoughts on the main 3.