I love both breeds, they're great dogs but I've also noticed the differences in the breeds that have been mentioned. I consider ALL well-bred herding dogs to be extremely keen and intelligent, of course their breeding has a ton to do with it, but both Shelties and Collies should be very bright dogs. Collies I've noticed are more friendly and inquisitive, but I've met my share of really laid back, friendly Shelties too! I think socialization and training has a lot to do with how they turn out as adults. Both should have enough energy to herd livestock all day, so I would consider both active dogs!