Enh, I kind of think Mikoto's too good for Touma. Then, I tend to prefer To Aru Railgun to To Aru Index.
Mikoto's a much better character when she's a more confident heroine in her own right than when she's just another tsundere chasing after a guy who's already got 12 other girlfriends.
"I will shove a lightning bolt up your ass and save my little sisters even though they do nothing but insult me in comically deadpan fashion" Mikoto is more fun to watch than some domestic bake cookies but never give them out girl.