What is the benefit of an ovarian-sparing spay? It seems like this would be a great way to avoid Pyometra but also keep the benefits of hormones. Ovarian cancer would still be a risk but I don't know the rate of occurrence on that.
An ovarian-sparing spay means that you still get the hormones. However, this also means that you still get the heat cycles. Removal of the ovaries generally causes the metabolism to slow down somewhat, which can result in weight-gain. Keeping the ovaries avoids this issue if it is a concern.
When I researched this issue in the past, it mostly seemed to come down to whether or not you were comfortable with your pet continuing to have heat cycles and whether or not you were comfortable with the hormonal/metabolism changes and potential weight-gain. Some conditions become lower risk with the removal of the ovaries (certain forms of cancer, for eg.). Some conditions become higher risk (eg. obesity). There did not seem to be a clear-cut "winner" from the information I read. That said, most of my research centered specifically around cats. There may be a more evident "best option" when applying the question to other animals.