It might not look great but it comes in handy, especially against Legendaries. I caught most of the R/S/E Legendaries in Timer Balls.I'd have to say the Timer Ball. I've just never really been a fan of it's design, I don't really like the color scheme, either. I'm also not a fan of the standard red and white either, because as stated above, they are absolutely everywhere.
Honestly? Heal Ball. It loses its usefulness the later you get into the game and I just don't like the color scheme.