IMO they are both the best and I go back and forth between which one should be #1. GSP has been more perfect and just complete in his own division but DC's accomplishments of beating everyone at HW and LHW is just too good of an accomplishment to dismiss. Of course you can say the shallowness of the HW and LHW division is why DC can't be #1, but GSP has never beaten anyone (except for matt hughes) with as big a name as Stipe, Dan henderson, AJ, Gus, Silva, and etc... If we made a top 30 list of mma fighters GSP has beaten maybe one other person on the list while DC has beaten prob 3 or 4. So who really faced the better competition. This is literally an impossible debate for me.