Soviet Union. The country which basically invented and implemented state-owned free healthcare on a very large scale (the USSR population was on par with the USA population).

And, frankly, I believe USSR succeeded in this implementation. I mean you can't make it substantially better than it was (taking technology advancements into account). It was great at preventing epidemic outbreaks, vaccinations, general population health, etc.

My sister picked up typhosus in a very remote part of the country, disease not known to primary care physicians for decades (well, they study it in medical schools but just like a historical artifact). But the system worked perfectly, she was diagnosed, sent to a special facility, got necessary treatment (and became a subject of research with daily visits of medical students from all across the city) and got out perfectly well (besides losing all her hair, but that part recovered quickly).

It's just everything has its pros and cons. And when you preach socialized state-owned healthcare, don't think you'll always be at the 'pros' side. Some people end up at the 'cons'. I'm not saying that my mother fell victim to this system, she fell victim to the idiocy. But the system made her suffer beyond what is acceptable in the civilized world.