My hair is very long (about the middle of my back) I have been coloring it med/dark brown for a couple of years. I want to go back to a med/dark blond. Which product Color Opps or Color Zap will be best for me to try. I cannot afford to have it done at a salon, I am always charged a lot more due to the length and thickness of my hair. I am wondering if one of these products will work well enough to allow me to follow with a regular permanent hair color in a dark or medium blond.

I'd try Oops first. Most people I know have gotten good results with it.

You're really just going to have to see what shape your hair is in after you remove the color. Don't color it if it doesn't look and feel healthy.