Out of the creatures listed in the poll? Probably mammoths, given their sheer size and muscle mass. I don't actually think dragons are as physically capable as some people make them out to be. They're strong, sure, but if they function like other flying creatures, their bodies are probably pretty light to keep the weight down, and thus make flight possible. Most of their muscle mass seems to be in their chest, otherwise they wouldn't be able to produce enough lift with their wings.
All in all, they're immensely powerful creatures, definitely a cut above anything else that was listed, but it seems to me that their power is derived from their ability to Shout, as well as their intelligence and flight capabilities.
Ogres too! I hate the ogres in Oblivion because they're so ridiculously tough.
Oh god, ogres used to terrify me. It stems from my first foray into an Aeylid ruin near Bruma. I was nearing a corner, and an ogre came running out from behind it at full speed. My poor little Imperial didn't stand a chance.