I don’t care.
I couldn’t care less.
I could care less.(informal)
I don’t give a damn.(mildly vulgar)
Like I give a damn.(mildly vulgar)
It doesn’t matter to me.
Really doesn’t matter to me.
Makes no difference to me.
Makes me no difference.(informal)
Makes me no nevermind. (folksy)
Makes no nevermind to me. (folksy)
Six of one ,half(a)dozen of the other. (informal)
Up to you.
Whatever you prefer.
It’s not important.
I guess so.