Learning English became a kind of mandatory, but it's not easy for learners to choose a single English to learn.
I'm an intermediate learner, and now it's time for me to choose an English from a certain land to learn and abandon the dialects of other areas in the world. Because I don't want my English bacame eventually mixed and always partly uncomprehensible.
So, which English is better do you think? And why? Please give me a piece of advice.
And I also want to know, with that English, what kind of life can people lead.

I would know better what to suggest if you told me what part of the world you were from and what your plans were.

If you are planning to go into international business, I would say to make your decision based on the area of the world you expect to be trading with the most. If you are from Mexico, for example, I would say that because of NAFTA and the dominance of the American economy, it would be best to go with American English. On the other hand, if you are from Ukraine and will be engaging mostly in European trade, it is probably best to choose British English.

Whatever you choose, however, do not think that it will make you incomprehensible to speakers of other Englishes. Most of the various dialects can easily be understood by people who speak others well. Most Am.Eng. speakers do not have to put a lot of effort into understanding a typical Br.Eng. movie (and vice-versa). There might be a couple of puzzling words, but it will not be a big problem.

Good luck with your studies, whatever you choose.

USA of course. Our country is full of opportunity, diverse, and can beat up any other country's dad. Agree with mountaineer.

Honestly, English is English wherever you go. The only differences between American and British English are very small. As long as you don't focus on hip hop or country music records, your English will be understood everywhere.

All types of English are comprehensible to one another. I don't see any reason why you should learn from only one type of English. The only differences you'll see are in spelling, slang, and pronunciation. Then again, with other languages, it's the same way.

With any dialect of English, I'm pretty sure you can lead whatever life you want equally.

I personally would advise you to learn as many 'forms' of English as you can, but if you can only study one basic 'form', I'd go for British English.

You can learn the other "forms" by watching TV.

probably american. most overseas learners of english learn american english because its the most internationally understood english accent and the accent forces you to really pronounce the words so people will be able to understand what youre trying to get across.

i personally learnt english in new zealand (british english), and the new zealand accent is difficult for even fluent speakers of english to understand so i faced some problems there. but other than that, it all went smoothly :)
just make sure you dont learn english is a texan accent/hip hop accent/something else extreme.

basic american english is good.

There are many dialects of English, and there are some that many native English speakers find hard to understand. But every English speaker understands Midwestern American English and BBC British English. So you can take your pick, which may well depend on who your teacher turns out to be.
There are also some spelling differences between American and British English, but they really do not present much of a problem.

There is only one English to learn, the proper kind. Neighborhoods pick up slang words. Once you learn English from school, you wil be learning the one and only way. There are places where you can learn English as a second language and often these schools are free.
Good luck. You chose the life you want to lead...