These are not in order.

1) Lightning Dust and Sunshower Raindrops
 
Why did I put these two together? It's simple: similar color palettes.
While the opposite of orange is blue, those colors on these ponies are tinted and/or warmed.
There's just something about these simple designs that I absolutely love.

2) Thunderstruck

This design is awesome. The slightly cooler hue of purple makes this pony seem more mature yet still spunky. Fitting for a teenager (lol).
The yellow streak in her mane matches with her super cool cutiemark and gives her more personality if the crazy hairstyle won't.
Her light blue eyes and dark pink eye shadow add to that seriousness.

2) Scootaloo 

To be honest, her design makes me nostalgic for the g3 Scootaloo.
I know she isn't a pegasus in g3, but I wish to talk about her anyway xD Sorry, Scoots

Let me know what you think. Did I let the g4 bronies down? (just kidding!) What are your favorite pegasus designs?