It totally depends what size artist you are.
Streaming is generating a lot of income at the moment, as is sync licensing, although the rates are going down and 'big syncs' are harder and harder to come by. Synch placements should be seen as a journey, rather than a destination, everything adds up slowly.
Publishing royalties can be huge if an advert is played all over the world on numerous channels for example. Publishing, when handled properly and accurately, can be hugely lucrative, but choosing the right publisher is key for the writer. Getting co-writes on songs recorded by popular artists can make a lot of money.
Merchandise can also be really beneficial for an artist, as often easy to cut out any middle men.