Colossus is stronger, after some of the guys at Marvel did some math, figured out that a 7 foot tall guy made of solid steel could never possibly weigh 500 pounds, they upped it to more proportionate statistics and gave him a strength boost to boot. Thing's strength seems to continually grow, as in the course of a decade, he's grown from 5 tons to 90 or so. Thing only has a rocky exoskeleton, whereas Colossus is solid steel, so Peter has greater endurance and whatnot.
As far as i know Things skin is just and exoskelton. His internal organs are not like his hide as to where colossus' is solid steel. Bones, eyes, lungs and so on. Colossus is no dought stronger and more durable than thing. It just makes sense. These two are two of my favorite Marvel heroes cause I tend to like the strong men of the Marvel U. So I have to pick one and its Colossus.
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The price of fame is high and the Thing cant pay the way.
I'm figuring they are equally strong. If there was any form of competition between the two, the victor may be the one with the better grip or leverage.
Grimm was mutated by the cosmic rays, changing his physical form, instead of regular epidemal tissue, he has a rock like substance, but he still has internal organs and stuff. I don't know if exoskeleton is the best term, as to me, that would imply that underneath he is normal. But though his physical form was mutated, it still retains the basics of human physiology, whilst Colossus is a humanoid piece of walking solid steel, with no organs or innards.
The Thing does not have human anatomy and physiology...colossus has organs' they r just made out of organic steel...his powers r mutant not magic...he has organs and systems that r still functioning...if his nervous system were not functioning how would he see, hear, or feel?