I would want to switch lives with AppleJack. I used to live on a farm and miss it dearly. So it would be awesome to live on my own farm! Also, she has a big family and I love big families!!! She basically lives the life I wish I could live right now.
My second choice would be Pinkie Pie. She and I are a lot alike, from the hyperness, to the randomness, to the friendliness (granted I'm shyer than her first, but still...)
Rainbow Dash would be awesome too!!!! Only because she is awesome!!! Also, It would also be neat to fly. I've always wondered how it would feel, to spread your wings and soar. To not have a care in the world. To see all the beauty from above... *sigh*
I don't think I could be anyone else really. Fluttershy is too shy, I love Twilight Sparkle and I would love to be her friend, but that's it. And I really don't care about fashion, so Rarity is out unfortunately.