First things first- as coconutty has said, there's questions of maintenance/spares, etc in addition to insurance and way more.
Each operator has a set or develops an operating requirement(s). From there, likely candidates are cast and evaluated for selection based on all factors. There is very little subjectivity when all the chips are down- operators usually will fly Bell, S, or AW airframes because they already have spares, operators, and maintainers familiar with said family of airframes.
'tis all getting too far from the helicopter & wrenches, and too close to the offices for my taste though.
