Recently stayed 4 nights here and another 3-4 nights at the SF Grand Hyatt a couple blocks up Market, so I figured I would compare the two. (Stays were back2back)
Used a suite upgrade at both locations - embarcadero suite (HR)/executive suite (GH).
Rooms:
Overall, the quite at the GH was a significantly nicer room than the embaradero suite. The GH suite had wood floors, two distinct rooms, and two bathrooms - one with a shower and the other with a tub. I thought the home automation lights and automatic shades were something unique. They completely remodeled the whole hotel in the last year and it shows. The HR room was dated and nothing more than a slightly elongated room for their normal king spaces. It did have a better view than most rooms, but I dont believe its really worth the spent cert.
Regency Clubs:
The regency club at the HR Embarcadero was significantly better than the Grand Room @ GH. The Regency club was the top floor that had views in every direction and at least 4-5x the food selection during all meals as the GH's offering, which was 1/4 of the 32nd floor. I did hear while I was at the HR that they will be repurposing that space into a conference area, so I suppose - if true - the regency club there will be significantly downgraded to a lower floor.
Walkability/Location:
Both are almost identical in location since they're like 6 blocks away from eachother. I did like being closer to the piers since all the stuck up people around Union Park's shopping tended to be a bit of a turn off.
Overall, I would probably opt to stay at the GH Union more than the HR Embarcadaro. The enhanced regency club just couldnt overtake the significant remodels at the Grand Hyatt.