I like steem-engine (@steem-eng). Being a market maker is very profitable since the spreads are huge. The online downside is that the trading volume is not quite high so best to only market make the bigger coins. And if you can't write some trading software it's a lot of work to put in orders manually all the time. Best thing is to write a trading bot yourself if you have the skills. I tried market making some coins manually as an experiment and it's not unthinkable to double your money every 2-4 weeks until you start to have scale problems. But doing it manually is just to much work and therefore not worth it.
Other than that, most dapps on steem are barely worth the time. Unless you consider making a few dollars here and there "great earning". That's not even a minimum wage.
I think the big money is in making your own successful dapp, like for example steemmonsters has done. Or when you would invest a considerable amount of money into a dapp and are a co-owner.
They vote posts and you can earn dlike tokens too. Spoke token has quite good potential so it's worth earning. You can also delegate some steem to dlike to earn more