If you can get (and afford) organic lemons, use them peel and all. The peel has powerful bioflavanoids and essential oils that are good nutritionally and as cleansers. Some people find the whole lemon too stong, however. If this is the case, use one lemon whole and peel the rest as you make your lemonaid.
It is all how you respond to the cleanse. Better to take a juice only cleanse than giving up.