Depends. If Earth or Pegasus Ponies, then Dragons. If Unicorns then Ponies. Generally, dragons have wings (at least the western style ones do), so do pegasi, but dragons have claws, sharp teeth, tough scales, and can breath fire. Pegasi ummm, do not normally have those things. Unicorns can do magic (well, more directly than dragons can anyway).
Of course, I'd rather meet a talking pony than a fire breathing dragon that may or may not want to CONSUME MY FLESH. Crisping optional.
Would you like to talk to animals? If so, what would you do with that power?