Serena was one of Ash's companions throughout the Kalos region and quite the Pokemon Performer.
Serena met Ash at summer camp when they were much younger. They reunited when Ash made his way to Kalos. She, like many trainers, was given the choice to select a starter Pokemon and begin her journey.
Instead of becoming a master trainer, she went the route of a Pokemon performer. She and her Pokemon were extremely close-bonded as they performed incredible dances and routines together. There are some great Pokemon she could have trained for that job.
Note: This article is subjective and reflects the opinion of the writer.
Top 3 Pokemon Serena should have trained in the anime
#3 - Masquerain
Masquerain may not be the best Pokemon in battle, but it is absolutely beautiful. This Bug/Flying-type would be a great partner for Serena in her various performances. It has four wings which allow it to hover and fly in any direction.
That kind of control and movement would allow Masquerain and Serena to pull off some glorious maneuvers and routines. It was shown during Gym Leader Juan's water exhibition and would have done Serena wonders.
#2 - Gardevoir
There aren't many Pokemon that are more glamorous and elegant than Gardevoir. It can create black holes, defy gravity, and so much more with its psychic abilities. Imagine how it could use those powers to create some awesome performances.
Serena never really had a powerful Pokemon partner to perform with. She did extremely well with the partners she did have, however. With Gardevoir at her side, the sky really could have been the limit for her goals.
#1 - Delphox
Serena selected Fennekin as her starter Pokemon. Eventually, she trained it enough to where it evolved into Braixen. Braixen and Serena were inseparable and had quite the dynamic when it came to their performances.
The anime series never saw Braixen evolve one last time into Delphox, though. Delphox is a Fire/Psychic-type who just perfectly looks the part of a performer. It is almost like a wizard with a magic wand. Seeing Braixen become Delphox would have pushed Serena further along in her performance career.