The fact is that each of these streaming services offers something beneficial to artists.
SoundCloud is certainly an upcoming website that has a lot of potential, but you have to know how to work each of these platforms to get the best outcome, and no two are exactly the same.
Definitely have your music on SoundCloud & Spotify, and if your music distributor (Tunecore/CdBaby) also throws in the other streaming services at no charge, why not have them on there, right?
Just remember that you cannot expect to make a fortune off of these sites. Even an artist who gets over a million streams on one of these sites, may only make a few thousand dollars. These are great for promotional purposes and to help grow your audience.
Be sure you equip yourself with a full music marketing plan instead of just relying on streaming income.