I was originally going to be a Chihuahua at first, but it didn't fit me very well. Then I toyed around with being a cat, but that didn't fit me either. But I eventually settled on being a Terrier because of Krypto the Superdog. There's a character on the show named Tail Terrier who ended up being my favorite character-, and actually, my fursona is literally just a recolor of Tail Terrier, but it's been stuck with me for nearly 12 years now, and I can't change it. XD
In all honestly, I kind of wish I had been something bigger, but I'm stuck as a Terrier and can't really be anything else. I wish I'd been a horse or a zebra or a taur of some sort. But as I said, I'm happy with being a Terrier as it's unique and everybody loves it. Even the name, "Matt the Terrier", rolls off the tongue nicely.