what dog breeds are known to be most healthy if there are any like these at all? OK I realize that every dog is different and even in the same breed there can be great variations of an individual's health. But is there a general tendency of more healthy and less healthy dogs? Thanks.
I don't think there is any real answer to your question. It's almost the same as asking, "Which race of human is the healthiest?"

All breeds of dogs, and all races of humans have their variances and health issues, even when everything about them appears to be identical.
If you want a healthy dog, take care of it well. Both physically and mentally. It's the owner's responsibility. Give it enough exercise and make sure it's living a happy life. There's no other way whatever breed you choose.
It's common for every single breed to have a genetic pre-disposition to a specific genetic defect or disease. There's no such thing as a breed of dog without any health problems. There are, however, some breeds with fewer and less serious potential genetic issues, for example Mini Schnauzers.
The best way to make sure your dog is healthy is to buy it from a very reputable breeder.
Beagles have almost been bred to not have disease, so they are considered one of the most healthy breeds.Everyone else on here doesn't know what they are talying about and obviously don't work with dogs on a regular basis.