I just stayed at both three weeks ago. Used a free night cert at the PH and points at HdL. Was upgraded to a junior suite at both. Didn’t use suite upgrade at either. (obviously not possible with a free night cert).
Aside from the location being better for the HdL, I would definitely prefer the PH, especially if using a certificate. I found service to be fine at both, breakfast at both was very good. Our room at the HdL was oddly shaped and didn’t feel overly spacious despite being a junior suite. The bathroom was far nicer and maybe double the size at the PH. The PH had blackout/noise shutters that closed outside the window and made the room delightfully silent at night. The train vibrations at the HdL were certainly noticeable but didn’t wake us, though something to consider if a light sleeper.