The Advent Calendar choice for today is Josephine Pullein-Thompson's Prince Among Ponies. Like Diana's I Wanted a Pony, this doesn't really focus on Christmas, although there is a mention. The whole glorious focus of this book is Adonis, the beautiful but wayward grey pony Patrick and Sara discover when they go and visit some family friends.
He is possibly the uber-pony gift (although there is of course Cascade, Tamzin's part-Arab pony in Wish for a Pony). Prince Among Ponies ticks all the Pullein-Thompson boxes - there's good and sensible riding set against the bash and point school, humour, and a good set of relationship dynamics.