Twilight Sparkle, mostly because I want her to do do less in big time two part episodes/movies and deal with more day-to-day anxious nerd problems. Or managing conflicts between people and having to make difficult princess decisions, and doing it in her dorky Twilight way. I loved Twilight in Testing Testing 1, 2, 3, but I felt like I hadn't been able to connect with her that way in a long time. I even remember thinking to myself "Twily, you're back :D"
Basically, less Fate of Equestria problems, more Twilight problems. That would make me a happeh boy
Funny enough, I'm kind of the opposite way. @Stellafera made a good post earlier that sums up my thoughts on Dash's ego very well.
Overall, I think Dash has a comparable problem with a lack of self-confidence than she does with arrogance and self-centeredness, as strange as it might sound. I get the sense that when she's saying she's awesome/the best/the fastest/(insert Rainbow boast here), she's trying to convince herself as much as anypony else. She's crumbled into a pathetic, nervous, desperate, defeated wreck too many times under pressure for me to say that her problem is as simple as being overconfident. I find the whole dynamic to be really interesting. And to Rainbow's credit, she's been showing a lot more of her caring, mature and kind side in recent seasons as opposed to the arrogant one. Yay growth
Whereas with Trixie, showmareship aside, she seemed to be enjoying what she did to Applejack, Dash and Rarity a little too much, and that rubbed me the wrong way. Which isn't to say that those three were faultless angels in that episode, but Trixie's behavior in that scene reminded me a bit of Dash in Fall Weather Friends. That being one of the times where I found Dash's attitude particularly grating instead of enjoying it for the cute bluster that it is. Dash's had some terrific character development that washed the taste of that episode out of my mouth a long time ago, though, and Trixie hasn't been as lucky.
To clarify, I'm more neutral on Trixie than anything and I'm sure I'd like her more if she got more screentime. Kathleen Barr has an amazing voice and I'm all about ham, which Trixie can produce in spades . I also think it's unfair of me to be hung up on one little thing that happened so long ago, especially since it tends to irritate me when others to that to Rainbow Dash , but I thought I'd throw it out since the subject came up.