Well, G2 Wingsong was my first ever pony so I guess she will always be the most special to me! She was also the first I bought again when I decided to rebuild my small childhood herd, so it was just like getting my old first pony all over again. I can clearly remember the times when I got my other 3 childhood ponies too.
Honestly though, I think all G1 or G2 ponies make me feel a little bit nostalgic, even ones I didn't have and all the ones that are years older than me... It's a little strange, it's like they bring me back to somebody else's childhood.