Jade of Livermere is one of the most prolific sires and consistently produces excellent puppies which is why he is in most cocker pedigree's,also Jasper of Parkbreck
Mike Smiths book on Working cockers and Springers has vast info on the good lines in cockers and is a great start for anyone wishing to research their cockers pedigree.
One thing to remember is that alot of cockers might not ne FTCH but that doesn't mean they aren't cracking working dogs, it just means they aren't trialled, however if there are very few FTCH in a pedigree there is no guarantee of working ability.
also I like Sealpin - Edward Martin's and Mailscot, which are Mike Smith's.
Health wise I know that Janices Rufus has allergy problems which are quite new in working cockers so it might be something to start considering, as with any breed popularity does not do the health any good at all.