I'll only ever go Pit if his arrows and side B will be better for the matchup.
I assume you play Pit more than dark pit, seeing how upperdash is objectively better than elecktroshock at killing. And since Pit has superior arrows in every way except damage.
But in all seriousness, I started playing Pit by accident. I remember back when I was 10-ish when I got brawl, I don't really like Pit, I hated getting hit by those arrows, and I thought his voice was obnoxious, namely because of his side-b. When smash 4 came out, I mained Robin, and my secondary was Mario. My friends really didn't like Dark Pit, and everyone was ******** about dark pit, so I picked him up as another one of my secondaries. I was starting to watch tournaments at the time, and one player that really struck me was Nario, I noticed what he was doing, like killing with f-throw and jumping with arrows, as well as other combos he did. Eventually, I took a break from smash 4, and by break, I mean I broke my 3ds... After getting a replacement a few months later, my Robin was complete ass, and I was losing interest in Mario. So I decided to just focus on Dark Pit, once upon a for glory match, I picked random and got light pit. And I immediately started enjoying playing pit more, I liked upperdash arm more, I liked his arrows more. Pit became my main and dark pit became a mere secondary. About a week ago my friend let me borrow his copy of Kid Icarus Uprising, and I LOVE IT. I marathon'ed it all last Friday and Saturday. I had major hand cramps on Sunday, but it was totally worth it. I've been clearing some of the challenges, even though it's not my copy. I plan to get my own copy pretty soon. And that, boys and girls is why I main Pit.