Colossus hands down.
Sasquatch can Press 70 tons which puts him up there with some of the strongest guys on the planet but Petey was lifting that as a teenager!
Also Colossus way more durable than the big furry guy and as for fighting skills Ive seen US Agent hold his own against Sasquatch and Agent nowhere near in Sasquatchs class strength wise.
I can also recall during the infinity crusade that he was glad Gamora took out the Thing as Grim was much stronger than he was and he couldnt have held him for much longer.
And I do belive that Colossus is at least in Grimms class now and more durable.