I use this one:
Amazon.com: Bamboo Deluxe Pet Shower Sprayer,...
It has a connector that fits in between the pipe that comes out of the wall and your shower head, and it is very easy to install. It only takes a minute and some channel lock plyers. After that, you can take it in and out of the shower using the quick connect fitting.
That being said, when I'm bathing the dogs using it, I do have to bend over the edge of the tub and it does make my back hurt. And I don't have a bad back. My dogs are too big for the kitchen sink, so I have no choice. My next house will have a big sink for bathing dogs, so that I can bathe them standing up!