James Chambers has produced a series of articles analyzing the health benefits (and cost-effectiveness) using the Tufts Cost-Effectiveness Analysis Registry. In these studies, he finds that treatments for rare diseases, specialty drugs, and those receiving expedited review are most likely to provide the greatest health benefit (≥0.9 QALYs gained compared to the comparator).
Chambers et al. (2020) shows that this is true for rare disease treatments:
Chambers et al. (2017) shows that this is true for treatments that receive expedited review:
and Chambers et al. (2014) shows that this is true for specialty drugs.
Keep in mind that higher health benefits are often correlated with higher drug prices. In the case of rare diseases, these highly beneficial treatments are less likely to be cost-effective due to the high cost of treatment. However, this should not be surprising as higher prices are needed to fund R&D efforts as, by definition, market sizes are smaller for rare diseases. On the other hand the Chambers et al. (2014) One study shows that while specialty medications cost more, the cost-effectiveness is comparable to traditional medications because, on average, the health benefits are greater.