What is the most easily treatable type of cancer?

The One Prevented. I have heard both basal cell cancers of the skin and certain types of thyroid cancer called "good" cancers due to their near-100% cure rate. However, i would consider the easiest cancer to treat the one prevented (by genetic testing and appropriate intervention); a close-second is carcinoma-in-situ (pre-cancers) found by screening exams (mammogram, colonoscopy, skin testing).
Basal cell carcinoma. Of skin. Almost all of these can be cured by surgical resection.