I have mastered the British accent spoken by the upper classes in Britain. It is called Received Pronunciation (RP).
Then I went to the USA, New York and researched American accents. What I have found out is that the most sophisticated General American accent is close to British RP.
I personally prefer British RP as it is regarded in the world more, but if you plan to live in the JUSA then I recommend that you master the General American accent. When I was in the airport restaurant in the USA and asked to bring me a fork the waiter could not understand me as I pronounced it in the British way
/fɔ:k/ without /r/ sound. Americans always pronounce /r/ sounds whilst British RP is not pronounced when producing three long vowels /ɑː/ as “car”. /ɔː/ as in “fork”, /ɜː/ as in “Sir” and in three diphthongs /eə/ as in “pair”, /ɪə/ as in “ear”, and /ʊə/ as in “sure”.
Another point is that Brish is more crisp because in RP consonants are well articulated. For example, in the American accent where the /t/ sound is between two vowel sounds as in “later” is pronounced as fast /d/ In British RP is a well-articulated /t/ sound.
I have developed and published apps for both British RP and General American.
You can it with the apps Elocution Lessons, Get Rid of your Accent UK1, Business English Speech and Fluent English Speech (British English) or American Accent App and Fluent American Speech (American English), and Power, Pitch, Pace, Pause. There are also two accompanying video courses: Get Rid of your Accent Part 1 and Get rid of your Accent Part 2.
The same apps are also available on Google Play. They are based on bestselling books in the series Get Rid of your Accent and have audio and recording buttons.