There are many varieties of English, not just British English (UK) and "American English" (USA) but also Canadian English, Australian English, New Zealand English, Indian English etcetera.
Which variety of English you decide to learn mainly depends on where you live, which variety of English you will need to interact with and the availability of learning materials.
In Western Europe, for example, people generally learn British English. (Since the UK is in Europe, this used to make sense.) However, in Russia (as far as I know) and China, people learn American English at school. In China, this is due to the USA's dominance in the world. If you live in Latin America, it makes more sense to learn American English, because you are more like to need American English than British English or Canadian English.
I also mentioned the availability of learning materials. For example, if you live in Europe and you want to learn Australian English (e.g. because you want to move to Australia) and you can't find learning materials for Australian English, it's perfectly fine to learn British English, since Australian English was originally based on British English. But if you learn American English, people in Australia should still be able to understand you. (In fact, most of the problems in understanding will probably be on your side.)
I can't recommend a specific variety of English because the choice depends on factors that aren't mentioned in the question. However, I would recommend making a choice and then being consistent in the learning materials you choose, otherwise your English will become a mixture of different varieties of English (e.g. a mixture of American English with something else). Here in Germany, people learn British English at school but they are also exposed to American English through films and other media; as a result, their English is often a mixture of British English (spelling, grammar and vocabulary) and American English (pronunciation and vocabulary) and they are not aware of this inconsistency.