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For me it is Partiko, Musing.io and BeScouted.

All of them serve their particular purpose. Partiko is a great way to work on Steem on my iPhone. BeScouted is very high quality photography oriented (think 500px), and Musing is a great Quora alternative.

Currently I'll have to say busy.org and esteem. I believe a dapp should be equally just in rewarding contents that's good irrepesctive of whether they're whales or minnows and that's why I think these dapps will go far to become the two biggest dapps for me.

However musing.io has shown potentiality, In just a short time of being here we've seen bright prospects, brilliant progress chances made and diligent reward of good question and answer which should be the focal for a dapp on the steemit blockchain.