Maybe I'm a little late to this question, but I'll answer anyway.

According to many sources, Pembrokes and Cardis are two distinct breeds, and may not have even originated from the same breed! (Though they don't know for sure). Pembrokes tend to be smaller, with slightly smaller ears, have docked tails, and are more outgoing and social than Cardigans. Pembrokes can come in several colors (red and white, and tri colored), and Cardis have more coat variation (they can be blue merle, for example). I've never had a Cardigan before, but I've read and heard they are more reserved than Pems but very sweet and laid back. Pembrokes are good family dogs, will bark (and bark and bark at times) at intruders or unfamiliar noises, and are super sweet and love to play. My older corgi Marta is 7 years old and still loves to play like a puppy!