Who would win in a fight between Allosaurus and Albertosaurus?

Allosaurus was 28 to 32 feet long and weighed somewhere between 2,200 and 8,800 lb depending on whose estimate you use. Tyrannosaurus rex was 40 feet long and weighed 12,000 to 26,000 lb. Tyrannosaurus rex would almost definitely defeat and kill an Allosaurus in a fight unless the Allosaurus managed to escape. Note that they never would have encountered each other, though, because Allosaurus died out about 97 million years before Tyrannosaurus evolved.