I visit HK 10 - 12 times a year, and these days I always stay at the R-C. I used to stay at the Pen, but although I really liked the rooms, I found the service to be pretty poor. Over perhaps 10 stays there, I was asked on 9 of them whether it was my first stay at the Pen. At the R-C, almost everyone I come across from the door staff to the check in people to the housekeeping attendants welcomes me back.
Service overall was spotty at the Pen. The rooms are nicer there, but I find the service incomparably better at the R-C. If you can get a room on the Club Floor for the same rate as you have at the Pen, that is well worth doing. Simon, the Club Manager, and his team do an excellent job, and the Club Lounge is a nice place to take breakfast and snacks. I have found the hotel very responsive to guest requests. A friend was going to stay there for the first time, so I told Simon about him and asked him to look after my friend. They really went out of their way to do so, and even upgraded his room. When I leave feedback about some aspect of the hotel, or a change in the service that I would like to see, they have responded to this.
Overall I find it a very welcoming hotel with excellent staff, and I have been happy to recommend it to many friends and family members, who have all enjoyed their stays there. Whatever you choose, I hope you have an excellent trip.