Steemit and Busy are both the same thing. They are just front-ends for the Steem blockchain and out of the two, I use a third option SteemPeak.com which offers best usability in my opinion.
As for Musing.io, I just found out about it a couple of days ago and ever since then my full attention has been committed to it. I just love how we can connect and find answers to all sorts of questions as easily and effortlessly as we do on Musing.io. I also enjoy sharing my knowledge by answering questions and learning new things by doing research.
Other than that I'm an hardcore gamer so I use Dlive quite a lot. Been streaming and building a community on Dlive for the past 7 months. Almost since the first day the dapp wen't live. Like Musing.io, I really enjoy my time spent on Dlive.io as its a very interesting and fun way to interact with the Steem blockchain.
One last Steem-based dapp I like to use is Dtube, commonly known as Steems version of Youtube. Even though I still yet haven't started my vlogging career on there, I enjoy wathing what kind of content other Steemins are producing and what kind of subjects are they into. A lot of interesting content can be found on Dtube and its quality is ever-increasing.
I don't interact on Steemit and Busy, anymore. My interactions here on the blockchain have moved to Steempeak, Steemmonters, Steemhunt, and Musing.io.
Steempeak has become my new go-to interface for the blockchain. This is where I write my posts, read other's posts, and make most of my comments and upvotes. It's a faster and more modern alternative to Steemit and Busy. So, it's my new default front-end. You should try it, too. It will can really improve your overall experience.
As for the DApps, Musing.io has taken most of my attention. I have a goal of writing everyday, and Musing.io has really helped me commit to this goal more. It's so much easier to go here, look for questions, and do my best to answer them. Granted, not all the questions here are great, there are some that makes me cringe just by reading them, but there are also a lot that I find challenging and interesting. Those are the ones that I usually answer. So, this has been a great place to practice my writing and broaden my horizons.
The two other places that has taken most of my attention are Steemmonsters and Steemhunt. With Steemmonsters, I spend a lot of time reading up about it, collecting cards, and joining contests that have Steemmonster cards as a reward. I will probably spend more time on it once the game is released, but for now my interactions are mostly preparations for the release of the game.
Finally, Steemhunt is a platform a go to when I want to look up cool new gadgets, eco-friendly solutions, and a lot of other tech developments. My interactions here are limited to commenting and upvotes. I'll probably do more soon, like write an hunt, but not at the moment. I
All of them differ with each other because they have a specialized purpose. Steempeak is a generic interface, Musing.io is a Q&A platform, Steemmonsters is a collectible card game, and Steemhunt is a product features place. This is actually what's great about the entire Steem blockchain--it has a rich content-based ecosystem with all these specialized platforms that everyone can use. It's not just a blogging platform. This way, people can find the places they think they can enjoy, contribute to, and benefit from and spend their time there.