The doctor has given you two options for root canal, both can give you optimal results if done by experienced hands. So the choice is entirely yours. Recent researches shows better results with motorized root canals. Regarding the number of sittings, it does not depend upon whether by manual or motorized rather it depends upon the amount of infection. So the decision of number of sittings leave on your doctor. Hope this solves your doubt.
Next Steps
Go for motorized root canal if money is not an issue.
Health Tips
Leave the decision of number of sittings on dentist.