It already has the best football atmosphere, fans/crowds, affordable ticket prices aiming the true fans/the working class, overall homegrown talent, enjoyable games of all of Europe IMO.
All it'd take for it to become the best is to at least 2 other clubs step up a bit. Premier League was United's league before the oil money came in.
The Bundesliga is by no means the best in every aspect, but they're certainly working their way up there. Now if only Bayern's influence outside the game gets properly handled back to the way it was 5 years ago.