All inventions have their its own merits . All are best inventions . So we can't say that only one is the best invention as every invention play a crucial role in our life .
But in my point of view Machines are the best invention of man.In the ancient time or past we had very problems in the farm lands says food take so much time to grow , ploughing etc . But because of these machines ( Tractor ) we can easily plough and the food gets ready in shorter period of time . Also these machines are used everywhere . We use air conditioners to keep our room cool , we use room heaters to keep our room hot . We use vehicles to travel long distances.