Which country is better to live after retirement between Spain, Greece and Italy?

I did not visit Spain, Greece visited Italy, UK and France

likes to know about them

Probably Greece or Turkey.

We have better doctors and health system than both Spain and Italy.

Italy of course!. Also CORFU was a BRITISH Colony.Some do not know the difference between English and British which offends many of us!!!!!!

Greece OFCOURSE 

We have better doctors and health system than both Spain and Italy 

Greeks live longer than Italians and Spanish 

All Greeks I know speak better English than Spanish and Italians 

Corfu was an English colony

Italy. One could live there forever and never die.

That really depends on your personality and preferences. I loved living in Italy, but it's not cheap.

Wherever you can get a visa / can afford to live out your retirement. 

If you're a UK citizen, you can no longer move freely as the UK is leaving the EU

None of the the above.  I'd be looking at Portugal.  The cost of living is very low, pretty much everyone speaks some English, and health insurance is inexpensive.  I plan on moving there for 6 months when I retire.  I'm sure if I will eventually settle there, but I want to go for 6 months at the very least. IF I HAD to choose from the 3 you listed, I'd go with Spain.  

That depends on a variety of factors, like how much money you have and what languages you speak, as a couple of examples. If, for example, you don't have a lot of money, Greece is going to be far more affordable than Italy and more affordable than Spain, but if you don't speak Greek, Greece is going to be tough because it doesn't have loads of English speakers, whereas if you do speak Spanish, you might consider Spain over Greece even though your money won't go as far.