I like all of them. Maple has her little issues with everyone. she actually thinks Sym might be too nice and was actively waiting for the other shoe to drop. Honestly Maple thought Rhapsody was the more even tempered of the three. That's likely down to more exposure leading to a bias.
I always liked Sym. Harmony was...well, let's be honest. She was fairly abrasive even before what happened to Rhapsody. But Static wasn't exactly Mr. Sunshine that night either...so glass houses and all that.
Harmony, she basically hides her true thoughts and feelings behind a sense of superiority, her near death experience as a child lead to her hiding behind a false sense of bravado, feeling like she had to be and act stronger then she was. Working in the fashion industry doesn't help much either. Harmony is probably the weakest of the trio and the least able to easily cope with stressful situations Similar to how it effected Rhapsody and her being overbearingly protective of anyone in her life, and overactive to even perceived threats. If I ever had a chance to bring Harmony back it would have revealed her being nicer then she acts.
Symphony was the balance between them, while she was shy, neverous and could scare easily, her unique gift kinda let her see stuff that others couldn't so ended up gaining perspective that would allow her to face her fears. Symphony was always the nice one, conceptionally the Fluttershy of the trio, to Rhapsody being Dash and Harmony being Rarity. What she was hiding wasn't anything that would have lead to any kinda personality change. It was that she was the reason Rhapsody and Harmony survived their ordeal as children, though she has never told either of them. She had felt it was more important that they believed they managed to do it themselves, least that's what she interpreted from her vision.
Also, not sure if this was ever revealed, but both Sym and Harm know Rhapsody was Black Night, and Harm actually designed her current look. This is why she took pot shots at Night Cap and his "cheap imitation" of her work more then just from Rhapsody venting about her coworkers to her. I actually had art about her redesigning it, somewhere.