I honestly thought that Celtic was by far the most interesting predator in the movie. Not just because of how incredibly bad@ss he looked, but his character just seemed so much better than Scar's or Chopper's.
Scar was just a 400lb kitten, & Chopper, well, he was admittedly much cooler than Scar, but practically nothing was revealed about what his character was like.
Celtic on the other hand, was the definition of bad@ss. The way he tossed Grid around like a paperweight & was able to hand him his @ss using pretty much his bare hands for the majority of the fight was awesome, & his character alone seemed much more menacing & interesting than Scar's.
In my personal opinion, they tried to humanise Scar a little too much. He was viewed pretty much as a heroic figure for the last 3rd of the movie. Wheras Celtic didn't seem like the kind of pred who would have just buddied up with Lex like that. He seemed much more deadly, more mean, & in a way, he seemed more like he preferred to hunt alone. He probably would have just left Lex there to fend for herself, & made his own way to the surface.
Obviously Celtic's mask looked awesome, but there was a great character underneath it aswell, that in my opinion made him so much more interesting than either Scar or Chopper. Admittedly, he did act somewhat like an animal during the fight, but in my opinion that was one of the cool things about him. He seemed much more primal & animalistic than the others. Rather than being like giant gladiators, such as Scar & Chopper. I would have defenintly preferred for Celtic to be the one who survived until the end, rather than Scar.