If sentient androids became commonplace would the world be better or worse off?

It is the future; humanity has not destroyed itself and created sentient automatons like Star Trek’s Data, would it be for the greater good, or make things worse? Men would not have to go down into mines to extract the ore the androids would do it. Capping blown wells like the BP well in the Gulf would have been a breeze, the androids could have walked under there and did the job, and they did not need air so they would not need diving equipment. Androids could have made quick work of the failed Japanese reactors. There would be many dangerous and hazardous activities that could avoid by using them. Even if they were sentient beings, would man end up enslaving them? Would there be a revolt as they took more and more human jobs? Would nations that could afford it have whole armies of androids? A fighting force will all the tactics of battle built-in. Night vision, super speed, endurance, never needs food or water, can lift 20 times more than an average man. A division of androids could decimate a human battalion in little time. Would they become smart enough or be programmed by rogue agents, to turn against humans? Would having sentient androids in the world make the world better overall or worse?