Best threaded headset ever? Shimano cartridge-bearing units from the 90s. Such as XT, LX, 600, Dura-Ace. Actually the 600 units were the best, in that they shared all of the same parts as Dura-Ace, except steel instead of the easily-damaged alloy crown race featured with Dura-Ace.
Before you commit to a headset, research what actually kills headsets. It is false brinelling. For every one headset killed by corrosion, I see 5 killed by false brinelling. Road headsets are alost exclusively killed this way.
It seems that Shimano was the only headset maker that figured out the solution to this problem. They can still be found on Fleabay. Just make sure you don't get one of the orphaned and useless JIS models.