Sorry, I'm at work and didn't get to finish my post earlier.
I think the reason I like these herding breeds so much is because they are not only beautiful, but also highly intelligent. I've never had a collie or sheltie, but I know that corgi's are very bright. Corgis also have the perfect mix of independence and family orientation. Ein is independent enough that he is fine while we are at work, even when it is all day. He just naps and plays. No seperation anxiety at all. But when I come home, he jumps all over me to greet me and gives lots of kisses and cuddles. The only time we have problems is when it comes to vacation. Corgis, by nature, are family oriented. They expect to be treated like everyone else. Which means Ein goes on vacation with us, because he is happier that way. He CAN be left with family; we just choose not to. (he lays around and sulks, but doesn't exhibit signs of nervousness or separation anxiety. He's just not happy being left out.)
Corgis just seem to be very well balanced in personality, are very intelligent, and don't require a whole lot of grooming. They are perfect for my family.
eta: They are also very friendly with strangers. Pembrokes love meeting people. I have heard that cardigans are a little more reserved with strangers than pems are, but I've never owned one, so I don't know for sure.