You can build a curbless shower that does not force you to step down, too. Called a barrier free shower (aka ADA). You may really appreciate that some day if you're ever in a wheelchair. I don't like a shower that has a step in it at all. I'd go with a standard curb or a curbless if it was my place rather than a sunken shower. this generally requires you to waterproof at least part of the rest of the bathroom floor, but that is easily done with readily available membranes (my preference would be Ditra and Kerdi www.schluter.com, but there are a bunch of others).