You must not learn an accent. Instead, learn pronunciation. Accent is something that you have with any foreign language that you'll or already know. But, I think that an accent is a good way to train ears.
Well, I like both (American and British).
I moved around the United States when I was young and when I was older. In my opinion, there are far more accents and creoles in America than people acknowledge. Additionally, there are those American Indian languages that were saved by live-in missionaries who created detailed written languages of the spoken language(about 400 died, but about 300 live on). Well, there is a lot of depth in a place that isn't touted as having much linguistic depth.
However... the most beautiful thing about American English is Noah Webster. He created a dictionary to prevent the English language from fraying into incomprehensible dialects... If you can get your hands on a print version of the Webster's 1828 Dictionary, that's as close to perfect as I think you can aim for.
Although probably not as ideal... I use a software version
https://victorybaptistpress.com/product/websters-1828-dictionary-cd/
but as I don't remember where I bought it, only what the software CD looks like, there's a link I found.
The website version... leaves a lot out. I don't recommend it over these other two options.