None has been shown to be superior.
A report issued by the Agency for Healthcare Research and Quality compares the effectiveness of treatments intended to reduce the risk of bone fracture in osteoporosis-bisphosphonate medications (specifically, alendronate, risedronate, etidronate, ibandronate, pamidronate, and zoledronic acid), calcitonin (a synthetic analogue of the endogenous hormone), calcium, estrogen (for women), recombinant human parathyroid hormone (1-34), selective estrogen receptor modulators (specifically, raloxifene and tamoxifen), testosterone (for men), vitamin D, combinations of the preceding agents, and exercise alone. The authors identified randomized, controlled trials demonstrating that the use of alendronate, etidronate, ibandronate, risedronate, zoledronic acid, calcitonin, parathyroid hormone (1-34), and raloxifene prevent vertebral fractures, compared with placebo, but they found no evidence of superiority among the medications. However, the report notes that sample sizes in the studies were small and might not have been sufficiently powered to demonstrate differences in effectiveness among the agents.
The crux of the matter. There is no documented evidence of the superiority of any agent used in the prevention of fracture in patients with osteoporosis.