Y is this even a debate? The answer plain and simple is anderson silva. Just look at the way he moves then name one guy in the division that comes close. Gsp is a good athelete but there are guys who can compete with him such as fitch,sanchez,penn all great athletes to. I would say jon jones might be second. However silva has the biggest gap in his division.
Reason y jones is not number one is the gap in his division is not that big...guys like evans can be compare. Then if you throw in anderson silva in the lhw division its very debatable. Jones is nice but silva is on a different level at this point. Silva speed/reaction time/accuracy is just outstanding compared to jones at this time.