James Brown has far more material than Marvin Gaye. Just between 1971-1973 James Brown released 9 albums, while his band, The J.B.s released another two albums. And one of his background singers, Lyn Collins, released a solo album featuring the classic Think, which features the drum break that Rob Base & DJ E-Z Rock used for It Takes Two.
If we're talking about who had a bigger influence it's James Brown. He created a new genre of music in which the drum beats were slower and more syncopated than the music that Motown was putting out. That syncopated drumbeat is best exemplified by the classic song Funky Drummer, which wasn't even released on an album. In fact, you could make a double CD of songs by James Brown that people sampled in the mid-to-late 80s.
Having said that, Marvin Gaye had a better voice and is responsible for the greatest album I've ever heard, What's Goin On
I voted for Marvin