I have a black shortspine urchin that loves the green and brown coralline I have. You could also get any other shortspine/pincushion urchin since they are all the ones common in the reef hobby are herbivores. Don't get a pencil urchin, they are scavengers/meat eaters and will often starve to death in an aquarium. Tuxedo urchins are also a good option and are good for smaller tanks but beware they will pick up unsecured frags and take them for a ride around the aquarium and usually leave them in spots where you can't find them.
My future big aquarium will have a halloween pincussion urchin or a couple of red and blue tuxedos :)