I voted for the deathclaw, purely because it follows that one law.
'The bigger something is, the better it is at sneaking up on you.'
Height-wise, the rest of the options are much smaller than a deathclaw, and don't have the same capacity for sneaking up on you/materialising right behind you. Getting the drop on a deathclaw is a rather uncommon experience, unless you're stalking them around Old Olney. Out in the Wastes, they will always get the drop on you, then drop you before you even turn around.
Bastards run too quick.
Feral ghoul reavers would take second place, but a few well-timed grenades usually sort them out for me.
Where the radscorpions are concerned, they're not exactly hard to outrun, and they lack the ability to climb, so standing on a rock with a shotgun renders you near-invincible.
As for the yao guai, I like to hunt those in my spare time. I don't know why, but punching a bear with a power fist is oddly entertaining.
The Glowing Ones aren't even worth adding to the poll, in my opinion. You physically can't struggle against a Glowing One.
The brahmin tied with the deathclaw at first, but then I discovered they lacked the ability to attack...and the mole rat made it into the finals, before I beat one with a stick and it exploded.
