Permanent or Semi?

So I have naturally red hair that I'm trying to dye back to the original color, I used to dye it blonde. I usually use the natural instincts dye because I thought it would be less damaging... but I hate having to re-dye it every 3-4 weeks. So I guess my question is: Which is more damaging dying my hair every 3-4 weeks with semi permanent dye, or dying it once every few months with permanent?