The far right.

Yup, far right.

Middle

one on the right provides a better contrast to the white but the middle woud be ok.

The middle and right colors both work with the shower curtain. The middle color is softer giving it more of a spa feeling. The right color is bolder, if you go with this color make sure your artwork is framed or matted in white.

Middle is more soothing, but far right is cheerful

Go with the middle. Once you apply the color on all of your walls, it will be brighter and a lot of green. I painted an entire bedroom of a similar green on the right. It was way to bold.... I regretted it. Consider your flooring, lighting and ceiling color.

If you don't prime the walls it will be difficult to really make a decision .
I have found this one for you

Middle, when it's on all the walls in a small space, you will be happier.

Middle color if bathroom is small. Right one if it's a nice size.

Middle one!

Agree with unwantedadvice.

I'd take your shower curtain into the paint store and see if they can colour match your "favourite" shade of green from the curtain.

I like the middle.