The research compared 50 cities on spa access, air quality, total number of nature and parks, sunshine hours, happiness and traffic congestion.
There are more than 240 parks, 698 health care centers and more than 2,000 hours of sunshine each year in Singapore.
The city-state also scored the highest on the list for happiness, reflecting the quality of life of its citizens.
Known for its meticulous urban planning and famously strict regulations against littering, Singapore is always rated one of world's cleanest cities. It was recently named the world's second-richest country in terms of GDP per capita after Switzerland by The Economist.
San Diego, in the U.S. came out on top in Holafly ranking, with a whopping 266 parks and nature reserves as well as 3,054.6 hours of sunshine a year.
Vienna in Austria ranked third. The city is known for its clean air, rated as having one of the best air quality in Europe.