I'm Kind of a Big Deal

When people start trying to claim complex people are "opposite" to each other, you already have plenty of reason to simply dismiss their point of view as being divorced from reality.Every pair of people has something they differ on by virtue of being different people. That doesn't make them opposites. Some people have "a lot of differences" and lack common ground. Some people have "a lot, but not quite as many as the last group" and maybe have tenuous ground to come together on. And so on, with a lot of nuanced gradients on the scale. If you keep going too far where you hit "there is very little actually different between the two" you'll eventually hit a stopping point where it is difficult to find meaningful differences.Regardless of where a couple lies on that scale, they might fall in love. Love is a fickle thing. If they lack common interests, they may find they don't have any activities they can do together and both enjoy. Some couples like that find sex to be the only thing they enjoy together, while others don't even have that. If a couple doesn't enjoy being with each other, love doesn't really overpower that, despite what the storybooks say.Those couples which seem very different usually still have things they've found in common, even if you as an outsider don't see them.There is also a concept known as "foe-yay" in which it is super popular to ship characters who are not merely "very different" but actual legitimately hostile to each other. Hero x Villain ships.I'd say RariJack falls high on the scale of difference. The fact that they are friends at all often feels forced. If they have common ground at all, it feels like they ignore it in favor of bickering. In areas that are important to them, they have different approaches and beliefs that turn otherwise "similarities" into differences (like both being business owners).When it comes to Trixie and Twilight (yay, finally on topic), canon has shown us that Twilight has held a grudge towards her. Even if she forgave her at the end of Magic Duel, she didn't forget. Her forgiveness wasn't, "OK, lets be friends and hang out now. Wanna get a smoothie?" Trixie ran off to try to salvage her career. When we see her again in No Second Prances, the two are downright icy to each other. Even by the end of that episode, Twilight merely agreed to step back and let Starlight have her own friends, and not meddle. She still never became friends with Trixie, let alone romance.So, all the work to get them past that "working out their differences" and so on needs to be performed by anyone supporting the ship. If you're writing a fanfic, you have all that to get past. That is the story you're stuck telling. In order to get past that to tell any other story involving the ship, you have to make a sequel.In contrast, Starlight x Trixie has a lot of that work done. They get along well, even if they have the usual problems friends/couples have. You can tell the same "get together" stories you can with Twixie, but you can also tell a story about a day in their usual life as a couple. You can address a lot wider range of topics.As an author, my interest in a ship is heavily weighted by that sort of concern. I like all three characters, but the better ship is Starlight and Trixie by far. They make a cute couple. Both are super interesting people. They have an appealing chemistry. Trixie has already stated she loves Starlight in canon (obviously intended to be platonic love, but we're shipping here, dammit). And best of all, you have far more variety of interesting stories to tell, without constantly going back to the "convince people" stage.As for anyone else to ship Trixie with, such as Maud: I was a fan of that series by Foudubulbe too. But you're either telling your own sequel to his work or you're doing your own version of his work (especially for non-Maud candidates). It's the same as with Twixie, only even more made up from scratch. You're not so much writing fanfic of stuff but writing your own original story at that point.Anyone is free to ship who they want for whatever reason. But the number of people who have made something actually interesting with that freedom are few and far between.