Best android phone under 300$?

I suggest you to pick either Samsung Galaxy S4 or the S5. They are really good, and they would be around 150 for the S4 and around 200$ for the S5.
Or, you can go with Chinese phones. They have really good price for the quality. I have bought Oukitel k6000 pro and it was absolutely wonderfull. Bit heavy, but the battery was 3 times more than an Iphone and 2 times better than Samsung S7