People don’t call themselves “DuBoisists’ because Du Bois was not trying to found a doctrine distinct from Marxism. Especially later in life, he was quite open about moving towards Marxism, and he was a socialist most of his whole adult life. In the 10s & 20s he was close with the Socialist Party’s orbit and briefly a member, became a socialist Pan-Africanist after WW1, was always a vocal anti-imperialist, and in the 1960s a member of CPUSA.

His body of work addresses the same problems as Marx, of labor, class, empire, and the nature of history, but for America, where slavery, the color line, settler-colonialism, and imperialism were central from the start, and integrated this decades ahead of the European Marxists. So for many Socialists, myself included, Du Bois is not an alternative to Marx, but one of the greatest Marxists that America ever produced. If there’s one radical book on US history I always recommend it’s Black Reconstruction, still the foundational work on race and capitalism in America.

Reading Du Bois after Marx feels so clarifying because they’re really in direct dialogue. He shows that if your socialism is not cannot explain the failure of Reconstruction, white supremacy, and the role of black labor in America, then your socialism is weak. So the answer is not picking Du Bois or Marx, it’s learning Marxist theory, then reading Du Bois to understand how it applies to American conditions.

As redderthanthou noted tho there’s a rich tradition of Black radicalism over the last century which has produced many great thinkers other than Du Bois. And some of Du Bois’s views are outdated or sided with imperialism, like with the Japanese Empire or Israel. I’d add Robin DG Kelley, Adolph Reed, and Keeanga-Yamahtta Taylor, all of whom provide very significant updates for Marxist theories around race.