I find shelties to be alot more energetic, playful, and focused. I find them to have more drive therefore making better workers. Collies are heading into a nasty place due to breeders who focus too much on looks. My friend (the sheltie breeder)'s mom bred collies but left the breed because the brains were being bred out of them -- and it's true -- judges keep asking for the eyes to be smaller and closer together. There is only so much you can do when breeding only for looks. I find that collies are much less shy though and better around people. Shelties are prone to shyness and nippiness, and they can be difficult to groom, but I've never met a collie that wasn't friendly or easy to groom. They are laid-back and very sweet. Overall, I would have a sheltie over a collie -- I would want something with more energy, drive, and speed.