If we start with revenue, I suppose the songwriting royalty in itself is probably the most lucrative, so whoever wrote the song.... Then their publisher would be the first mainstream in royalty. After that there are performance royalties or neighbouring rights as well. Those are royalties that would be due to people performing the music but who didn't compose it. Then there would be live touring. Probably now in the digital age, live-playing revenue is the most important source of revenue and probably the largest, especially for independent artists, because revenues from recording royalties, streaming, and physical sales are so low.
On May 7th, 2018. See this statement in context.