People are different. Some like it hot, some like it cold. Some like orderly societies, others enjoy a bit of chaos. Some are obsessed with good food and wine, others don't much care what ends up in their stomachs. Some like to be surrounded by fellow expats like themselves in gated communities, others prefer to blend into the local culture.
There is no one-size-fits-all best place in the world for everyone to retire. (And if there were, it would get crowded very quickly).
The real questions is: where is the best place in the world for you to retire?
And that depends on many factors, such as what you enjoy doing (e.g. surfing, snow skiing) and don't enjoy doing (e.g. drowning, getting frostbite). It also depends on what you can afford, your ability to learn new languages, and what you want to do in your new home.
Retirement is not death, or at least it shouldn't be. When you move to your retirement paradise, you will quickly discover that a 24 hour day is exceedingly long if you have nothing to do. You will need to fill up up those hours with activities you enjoy, and that will influence where the best place is for you.
So, what have we got now? We have several criteria to be applied in choosing your retirement home: Ask yourself:
1) What are my likes and dislikes? What is important to me?
Make a list of the things that are important to you -- warm sunny weather, friendly natives, bird-watching. Then make another list of countries that fit with those likes and dislikes. If you hate seeing graffiti on walls and chewing gum on sidewalks, your list should include Singapore, because in Singapore you can be whipped with a cane for vandalism and thrown in jail for leaving gum on sidewalks. On the other hand, if you are big on personal liberty, Singapore is probably not the place for you. Similarly, if you are a Mormon missionary, you should probably not consider Saudi Arabia; and if you are a nudist, France is a better option than Iran.
2) What do I want to do when I retire? How am I going to spend my time?
Golf? Hiking? Cross-country skiing? Reading your Kindle? Surfing the internet? Sitting on a beach? Make a list of countries that excel in the activities you want to pursue when you retire. If you are a sport fisherman and live to catch yellowfin tuna, then Panama would be a good bet. If you are an avid cross-country skier, then Canada and Norway should be on your list.
3) Where can I afford to live when I retire?
There are lots of fabulous places to live on this planet -- Lake Como or Florence (Italy), Paris or Nice (France), NYC or The Adirondacks (New York), Laguna Beach or Marin County (California), Barcelona or Ibiza (Spain) . These are all great places -- if you can afford them. If not, you will need to start thinking about other wonderful places with lower costs of living. This is the point at which places like Panama, Costa Rica, Mexico and Thailand come into view. These countries all have areas where English speaking expats live and thrive in substantial numbers, and they are all relatively inexpensive.
4) Can I learn the local language?
Understanding the local language is important for two reasons. First is the practical one that you will need to get around and do stuff in your new country, which is hard to do if you cannot talk to people (waving and pointing has distinct limits). Second, you will never really understand the local culture if you cannot speak the language.
Some languages are harder to learn that others. Spanish is relatively easy. Mandarin, Thai and other Asian languages are very hard for most westerners. This is one of the main reasons I moved to Panama instead of Thailand, Cambodia or China, which I also love.
You are now at the end of my short rant, but you are only starting the work you need to do if you want to retire overseas. You will need to consider a host of other factors that depend on your personal circumstances.
Are you healthy or do you have medical issues? If you do, then you may want to consider Panama, which has excellent health care, but not Cambodia, where you can die on the street and no one will notice.
If you worry about crime, Honduras is not the place for you (highest murder rate in the world) but Thailand would do nicely, as would Canada, England or Japan, which all have very low rates of violent crime.
Now is the time to start thinking and making your lists. Do your homework. Do not rely for all your information on businesses that make money pitching one destination or another, or organizing retirement tours. If you are interested in a particular country or region, read everything you can on the internet. There is an enormous amount of information available on the internet. Use it. Make yourself the master of your own destiny. Start figuring out which retirement location is best for you!