The overrall climate among current faculty and grad students is something I paid a lot of attention to. How well the department got along, as well as how much you get along with your POI and their lab group is super important considering the amount of time you will be spending with them!
Also, this depends on what your preference is, but I personally wanted to work with a lab group/advisor known to be collaborative (with other faculty within the department and within the specific field of study). Networking is such a huge part of academia, so having an advisor who already has these relationships established is super helpful.
Lastly, I did not use this is a critical deciding factor, but I paid attention to what types of clinical experiences (including externships) they offered because I want training with a specific type of population.