Hello.
Use Play/Stop Events to stop the Music or setting States using Event Actions? If setting States, look below.
No, certainly not. It really depends on how you want to "manage" it in your production, and how much visibility you want the game side to have. Let me exemplify...
Setting a State directly
If you set the State directly from the code, you will have visibility from the game, that you are setting a State. Maybe you have a Wwise-Type State, that ensures only States can be selected. Or maybe you are just setting States with text, so you avoid having to make numerous Wwise-types for each State, but just send the name of e.g. the region.
Setting a State using an Event
If you set a State using an Event Action, you will technically achieve the same thing, but the visibility from the game will only be the name of the Event (which might be good to simplify it for the rest of your team). This approach also has the benefit of being able to manage your Event Actions in Wwise without having to do any changes in the game. For instance, say you've made a "Player_EnterVillage" Event, which is setting the State to "Village" and you later decide to set an RTPC from that same Event. All you need to do is add another Event Action, generate new SoundBanks, and voila, it's in the game.
So which method is best? It really depends on your game. Your question raises a very important point when integrating sound, which is to consider leveraging Events and Event Actions to retain sound controls on the Wwise-side of things and hereby be able to work more independently from the game engine.