
"Rage" is characterised by unprovoked, unpredictable aggression, and a dog that appears to not know where it is or what it's doing (almost in a trance, glazed expression), and "snaps out of it" after an attack. Genuine cases of this are rare and if they do happen, are down to medical reasons - this can be epilepsy, hypothyroidism, a brain tumour or even food intolerances (had a case of that last year).
Very often what is described as 'rage' in cockers is actually resource guarding, and often it has become harder to predict because the owners have punished the dog for growling (communication of discomfort), so the dog has started to skip to a snap or bite. But because of the 'rage' stigma, often that is diagnosed without the dog even being seen and assessed, simply because it's a cocker.
They are prone to resource guarding as a breed so the right handling from the start is important (not taking things from them without swaps, training a good 'leave', sufficient mental stimulation etc). The communication issue can happen with any dog though, and not just with resource guarding - I've seen a husky/malamute crossed diagnosed with it and in reality, he was under severe stress due to inappropriate living situation and handling, and he had been punished for communicating his unease by growling and showing his teeth. So he skipped to biting. The only case I've seen that comes close to the true "rage", if there is such a thing, is the above case of food intolerances and that was in a shih tzu/lhasa cross!
In general temperament terms, I think a golden would probably be better suited to your requirements but they can be a handful as pups sometimes, as they love everybody. But calm, consistent training will win through, as with any dog. I would do your research and meet dogs from various lines to find the temperament you want. I know one absolute loony golden who has been very hard work for his owner to raise, and the entire litter were the same. Cockers can be lovely little dogs, and taught to chill, but on the whole I find them much busier than goldens. Working type cockers do need a lot of input as they still have that drive to do a job all day. They can be very rewarding pets, but take a lot of work to meet their physical and mental needs (mental mainly, they are very smart little dogs).
Healthwise both breeds have their issues as all breeds do, so again, research is key, as is finding a breeder who not only does all the health tests (not just what the KC asks for, but all available), but who also acts according to the results. No point finding out a dog has a high hip score if you're going to ignore it and breed from them anyway!