Buy the correct wrench... a thin six point box wrench (dirt bike axle wrench) made by Motion Pro. I have a LOT of tools, but that had to be added to my arsenal for my TX750. Nothing else would work in there. The stubborn ones came right out (even though they were fairly well bitched up already) with a thump of the plastic faced dead blow in this wrench, no more drama.
Some knuckle dragger had tried the above mentioned hex rounding methods before. Here's the center punch method that was ineffective.
and some other mouth breather's handi-work: