Great question for your first post! Welcome to Salon Geek.:hug:
I notice from your profile that you are already qualified, so am assuming you are looking to do a conversion to either NSI or Creative.
I'm an NSI technician, but... that doesn't mean i prefer them to Creative. They are both leaders in the field, so my advice would be to research both courses, because there are differences. Training centres/availability was also a factor for me. See which best fits your individual requirements.
Good luck
Lisa x