My favorite breeds of horses would have to be Thoroughbreds, Friesians, and any of the heavy draft breeds. For my first horse, I'm hoping to get an Off-Track Thoroughbred; I just love the breed's courage and boldness and heart that strives to please.
And as far as the reasoning behind Friesians and drafts, I have an obsession with anything England related, and I love studying the medieval periods. Just the thought that those amazing horses once rode into battle with a knight literally covered in armor is just awesome. I also love how elegant and regal they appear to be.