Only the truly royal are allowed to sit in a relaxed manner in olden times. I'm calling this as still royal.
I put crystal because with a name like everypony, it's probably good to even include uncommon races (and not just the super powerful one). Though bat ponies are uncommon too, crystal seems to just exist in that one small empire, that until recently wasn't even visible to the rest of equestria.. A breezie could be interesting too but I'm guessing this was made before that.
I feel the Earth pony is the best option because it's basic, and any race can be made from the Earth Pony Base. That being said, I also feel it represents neutrality, something we pride ourselves in having. The Earth Pony would show that we can tolerate anyone.
It's official! Our new mare is going to be a Unicorn! Now, I leave it up to you to come up with a name, while I get started sketching a few body types to choose from. http://www.everypony.com/forums/showthread.php?14837-Everypony-Mascot-Discussion-3-Name