Four strategies I would use to make sure what I buy is the best, I would:
-Decide on what form it comes in (gel, foaming, bar, etc.)
-A gel or foam option would be the best, and the foam helpes reach into the tissue better. A bar of soap harbors more bacteria.
-Price
-It will need to be in your price range, and you'll probably want it to be on the cheaper side if it's something you'll use a lot.
-Exfoliants
-Exfoliants are a great additive, and they help cleanse the skin But, make sure it's environmentally friendly, as plastic beads can clog up pipes.
-Moisturizers
-Another great additive. This helps keep your skin moisturized, and even better, healthy.