I rented a one-man PHD back in 2016 when I built a deck for the hot tub, and I have a SSQA Land Pride HD25 with three augers including a rock auger, but have zero experience with a 3-point PHD. The reason is that I would never have bought a 3-point PHD for a number of reasons. To me they're less than ideal and need near perfect conditions to be of any use.
I would say that if the ground is hard, and nothing is harder than rock, a rock auger is the way to go. I've tried punching holes in the ground here using a 9" auger and it's a joke. The 6" rock auger does an amazing job but you have to go slow. A PHD that uses an hydraulic pump and that is mounted to the FEL is so much nicer to use with far more control with the ability to reverse rotation and adjust auger angle with ease. I would also add that a gear drive tractor trumps an HST when running a SSQA mounted PHD.
The takeaway here is that the choice of auger can make a big difference, and if members here are considering a PHD, look closely at SSQA hydraulically powered augers that can run off the 3rd function. When sized appropriately they're extremely effective.