Hi, I'm a new forum member, thanks to my brother (one_cat) who's a DIS addict. Anyway, I show and breed dogs and thought I'd take a stab at telling you some differences in the breeds, and also what to look out for when choosing one.
CKCS are of course smaller, very sweet, and very affectionate. They do not require as much grooming as a cocker, but do need some. They are a new breed in this country, and thus less popular, and a bit harder to find. Cavs suffer from patella (knee), eye, and also severe heart problems. A reputable breeder will have screened for these problems in the parents, and also generally screened puppies against heart problems. They also will guarantee your puppy.
Cockers, are really very overbred. It's easy to get a bad one, hard to get a good one. However, there are many reputable breeders out there breeding for temperament and health, it's just finding them. Cockers should also be screened against, eye (major problem), heart, knee, and hip problems. Again, a good breeder will show you documentation, and also guarantee the puppies.
If you visit
www.akc.org you can find the links to the national breed clubs, which will send you literature on the breed and also a listing of reputable breeders in your area. They can help you decide which breed will be better. Most breeders are happy to have people come and meet their dogs, and see the breed in person. You will have to get onto a waiting list for a quality puppy.
Hope this helps you a little.