Depends on the time and day, being a GOAT is a bit different from being the best fighter at any given time. As I said earlier, Ubereem at his prime, IMO, would have steamrolled Fedor in his, but his accomplishments are lacking so he obviously can't really be a GOAT. Ngannou is probably the most dominant HW of the last 10 years and could very well beat many fighters people consider to be the GOAT but himself has yet to establish a legacy that could put him in contention. It's kind of a combination of Legacy, Dominance, Opponent Quality, and Accolades. My favorite HW is Stipe who certainly has the record and accolades to back him up but obviously he's 1 and 1 with Ngannou as of this comment so his position is definitely able to be disputed, along with the questionable quality of most of his opponents. It personally comes down to preference IMO, I don't have a definitive GOAT and I don't really think it's possible to have one objectively if the field is so competitive.