I liked almost all characters from the first moment on. Same with Starlight Glimmer. My feelings for her developed slowly over time. When she returned at the end of season 5, I was so happy! And then she even became a part of the main characters in season 6! This is the moment for me where FiM really started to shine for me and a lot more depth was added to the show. With every moment Starlight was on screen, I liked her even more and more! To me, she is the most realistic and relatable character from...basically all media I know, not only FiM.
Starlight is also just such a balanced character. She is not purely evil, not purely good. She isn't as extreme as many other characters or who stick to one or few traits. She is honest, she lies, she can be annoyed or be super passionate, she can become angry or furious, but also show the most beautiful smiles, she is caring and kind, but can also be the worst enemy, she likes to impress sometimes, but the same way she can be happy for others. And I love all of that about her. She never annoyed me or anything. She never did anything I would hate her for. To me, she just makes sense. I think there was only one moment where I wouldn't side with her, and this was when she gave away Trixie's wagon. Was it worth it though? Yes! It led to more unique and fun moments.
With Starlight it simply never becomes boring. I'm a similar type of person, I can't just stick to one thing for the rest of my life. Okay, okay, besides FiM! I also like animals and nature like Fluttershy, tea parties and picnics as well. But it would depress me to do this almost every day. For this reason, I can't entirely relate to the main characters, but only to some aspects of them. I see myself more as a creative and adventurous person, I need variety, every day. And Starlight is one of the few characters who would enjoy to do about anything.
I tend to like side characters more than the main characters. A very good example is Minuette. She is not as extreme as Pinkie Pie, who would throw a party at every moment of her life, if possible. Minuette is a very happy and positive pony by nature and you can talk to her normally, she will be very quiet and listen to you. She doesn't sit on heated coals. It is unknown what her cutie mark means, but she most certainly isn't a character who only stares at hourglasses the whole time. I like other characters more than the Mane 6 for example, because I can connect to them on various levels and not only one or a few. And this is the most important factor for me. And Starlight (as main character even!) has it all. She's absolutely perfect.