In the case of choosing between Riverside and StreamYard, then it depends on what you want to do. Riverside is preferable in case you attach importance to good recordings - it provides you with individual audio/video tracks, 4K video, and good editing software. It works well with podcasts, interviews or anything that one would wish to edit and groom later.
StreamYard is, however, simpler when you merely need to go live fast. The interface is very simple, and can work with the livestream of YouTube, Facebook, and Linked In with minimal set up. The disadvantage is that recording is not so strong and you do not have so many means of editing.
Personally, I would choose Riverside in case you want to create professional content, whereas StreamYard in case you simply have to stream live without worrying about particularity.