I've been in Bali for more than three years and frequently get questions regarding hospitals.
I've had fully anesthetized surgery at BIMC and all went well despite a black out while it was in progress. The cost was about 70% of what I would have paid in Singapore. The hospital is world class with that the priciest in Bali but the place to go if things are complicated.
Siloam is the up and coming hospital in Bali, prices are good but the pharmacy is a rip off, go elsewhere to fill the scripts they give you. My wife spent five days there following a broken ankle and it seems to be the most frequented by westerners in motorbike accidents in Bali, I saw several come in each day. The surgery went well and it was complex.
I've also been here for MRI's, Check Ups, Blood Work, and common things like Bali Belly, Asthma, and Dental. They're good but not awesome. Awesome for me is Singapore but alas I live here.