You have to consider what you are doing 80% of the time. When we bought the first 257B, I originally inquired about the 277. the salesman, who easily could have sold us the 277 went around to our jobsites, saw what we do most, and brought the 257 for a demo. At the time we had a T-190 Bobcat on the same jobsite. The biggest reason for the 257 was access. the 277 would be sitting idle more often. The second reason was trailering. A 277 can't really be pulled efficiently with a tag trailer and a pick up truck, you really need a gooseneck, and then pulling that trailer with a medium duty (45-55-6500 GM, or heavy duty truck (Mack Vision) is not possible.
So, we went with the 257's for that reason. Ask yourself what you do most, and what you are using to deliver the machine to the jobsite with before you lock into one.
It's probably the smoothest ride of all track loaders, with bogie double bogie and the rocker roller system it uses. The width and weight will limit you. As far as Cat and HP, if I had one critsizm it would be pertainate to HP. And even with that, the machines will do anything we ask of them. All high hp does in the size machine the 257/277 does is allows to be placed on the nose more often.