I consider small cities to be more livable than large ones. I grew up in a small one, unfortunately now of a large size, and probably didn't appreciate it enough at the time. There was a downtown core, easily accessible by bus or car with free or almost free parking.
Big cities today have a certain qualities in common and generally I don't find them to be positive ones. The traffic can be horrendous both within and upon approach. The number of vehicles seeking to enter the city containing commuters on their way to work is in excess of the carrying capacity. Invariably the roads have not been added to nor increased in number or width. Transit has not kept up with the demand for access to the city by the outlying suburbs.
Big cities in Europe tend to get a lot of tourists, especially in the summer. It is easy for local residents to get fed up or at least frustrated with the added congestion. Expats moving to foreign cities can also have the effect of driving up real estate prices beyond the reach of the local population. I was surprised to see a recent segment on a television program called International House Hunters wherein the price of an albeit large condo near the beach in Puerto Vallarta was close to $800,000.00 U.S.D. The average salary for a Mexico worker is, according to my brief research, around $400 to $500 a month. Of course, there is considerable variation with airline pilots being the highest paid employees and Mexico City workers are more highly compensated as are employees of foreign companies. But my point is that these beach side condos tend to be built for an overseas market.
I've read recently that housing in London, a city that I do like, has gone up ten to twenty percent in price in the past year as people consider a house or apartment there a better investment than a bank account. Meanwhile, the workers needed in the City can't afford to live there.
Livability is an issue around the world it seems.