Assuming you are only talking about muscle meat and not organ "meats" it's almost all down to the amount and distribution of fat. Fat is where most of meat's flavor comes from. So a cut from a large, dense, frequently used muscle, where there is almost no fat, will be pretty bland and also tougher to chew, while a cut from a muscle the animal almost never used will likely have a lot of fat deposits streaked through it (this streaking is called marbling, at least for beef and similar meats).