Its an interesting question to ponder. I mean when you naturally look at the mane 6, the obvious one that stands out and could be the best overall princess is Twilight bar none. She fits the perfect mold of what a princess should be in my eyes. Twilight has the leadership quality in her, as well as the organizational quality. She also has the modesty factor which would make her well liked as she would prefer to be put on the same level as anypony else, despite her now newfound royalty.
I do understand the arguments made here though, but I always had a kind of inner feeling while progressing through the series that this would happen eventually. Everything had slowly lead up to this. I remember Faust saying that in the end Twilight would become a princess.
As for the question itself, I'm sure Twilight had some dreams and such about becoming a princess, but probably doesn't want to be looked up to as a figure of importance like that. Her modesty counteracts this, even though in the long run it might be of great use as a princess, and she still looks quite uncomfortable and a bit scared even at the end of MMC.
We'll see what happens though.