If the rainboom didn't happen-Twilight SparkleMore Like This
Some people might not agree with me that Twilight wouldn't be that effected. Her life certainty would, she wouldn't be the prize student of the princess! I know that would change, but I think this would just encourage her to keep studying even harder. Many things would change though.
1.She wouldn't have Spike. (Saddest thing ever)
2.She wouldn't know how much magical potential she had.
3.Because of number 2 she would probably doubt her magic abilities and not practice magic that much.
4.She also would have never moved to Ponyville.
Despite all this I think she would still be an "egghead" and love to bury herself in research on how to amp up her magical powers. She would probably be a lot less sure of herself and bossy.
Her cutie mark would have changed because she wouldn't know about her super strong magic. I have know idea what it would be (a book maybe?) and would love to hear your suggestions.
All these reasons are why I think Twilight Sparkle would be the second