This has been dealt with lots of times. I spoke to the Bell representative the last time this came up and he said there is no reason why one should fly from one side or the other apart from where they choose to site the starter and useful switches. There is no aerodynamic reason, the c of g has nothing to do with it and the direction the rotor turns makes no difference. In other words the manufacturer decides where they want the pilot to sit and puts the starter and switches that side.
Instructors sit the other side to the student who sits in the P1 position. The student starts the machine but after that it makes no practical difference where anyone sits.
Regards,
Chopperpilot47