That's a tough call. In today's NFL, I'm taking Mahomes, no doubt. Brady did it in an era spanning fashion. No, he probably wasn't the best QB of the smash mouth era, nor is he the best of the current, highly protected era.
But, his success spanned both eras. Impressive as hell.
Right now, many wonder if Mahomes' success is attributable to Reid, in the same way they wondered if TB owes his success to BB. TB had just a sliver of time to prove that his success is not solely due to BB. Mahomes will have a much longer post-Reid career to prove it.
He may need to lock down one more ring with Reid, to have a chance of achieving Brady's total.