These aren't in an any order. 

1) Twilight Sparkle
  
The more I look at Twilight's design, the more I like it.
Darker colors, especially purple (which is more pleasing to the eye), may indicate seriousness or wisdom.
The lighter streaks in her mane and tail is what makes this character design recognizable and complete.

2) Sugar Belle
  
Ah yes the face of my pfp. There's no doubt that I like this horse.
Her curly, dark mane, bubblegum pink coat and darker pink eyes tells me that she's cute and fun to be around, but she knows when to be serious.
I also like how her entire color palette matches her cutie mark (with little yellow sprinkles to balance it out)

3) Fleur de Lis
  
No doubt that Fleur is gorgeous. I love the very light pink mane colors, her purple eyes, and the fact that the shadows and outline of her coat are purple.
I even like how her cutiemark has a light yellow color to balance things out.
Don't be too fooled by her pretty appearance, for within her eyes is wisdom and pride.

4) Flurry Heart (art by SpindleSpice)
  
I know she's not a unicorn, but I'm not going to make an alicorn design blog entry.
This design is super cute yet very fitting for the baby princess of the Crystal Empire.
There's love, gentleness, playfulness, and wisdom radiating from the color palette.

Let me know what you think. What are some of your favorite unicorn pony designs?