I've been using minnowbooster to boost my posts but since two weeks they are giving very very poor return which is pretty lower than 10% at present it's just around 4% which gets low when steem price go down over the period.
But, there's another way to earn pretty good returns if you delegate your Sp someone like @invinciblelight who is going to launch his upvote bot tomorrow. I am getting pretty good returns per day from my delegation. ☺