I was never in Royal Suites, but stayed both in Citrus Suites and Adelphi Suites. I always book a larger room: One Bedroom Suite in Adelphi and One Bedroom Executive Suite in Citrus. Both are approximately at the same price: 3200-3300 baht per night now (it was at 2500 before). Both are large (50-60 sq meters) and good for taking photos (important for me), since the walls are painted white and the furniture is in light colors. Both hotels are in the same category: 4 star hotels.
Adelphi is on Soi 8 and more easily accessible for taxis. Taxi drivers do not like to go to the Soi 6 hotels, as Citrus Suites of Park Royal, because they get stuck in the Soi 4 mess in front of Nana. Citrus and Park Royal are closer to Why Not and Nana Plaza, but the walk through Soi 6 from Adelphi is not very longer. Adelphi is closer to Check-In and Cindy's Secrets.
When you book a room in Citrus Suites, ask for a NON-LEAKING shower. Many of them are leaking and create a flood on the floor of the bathroom.
Both Adelphi and Citrus are frequented by the same clientele: half of them are families, the other half are mongers, many of them taking ladyboys. Unless you come with a ladyboy in the afternoon or early evening, you do not cross the families anyway and if it sometimes happens, you do not need to worry about it. The staff in both hotels is ladyboy-friendly and they have seen it all. However, if you had an ass-penetration accident in your room (shit happens ), do not forget to give the housekeeping a tip. They are paid for standard cleaning of your room, not for cleaning of this kind of mess.
Both hotels do not enforce the LB to leave her ID / passport at the reception. However, it is for your own protection. If something happens, you have much better options if your misbehaving LB left his ID downstairs.
You have more good options for dinner on Soi 8, therefore Adelphi is a better choice in this category. Also ladyboys, at least those from Check-In and Cindy's, prefer going to Adelphi Suites.
Before I prefered to stay in Landmark, which is a 5-star upscale hotel, but they started to ask silly prices, therefore I changed to Citrus and later to Adelphi. If you want to impress your LB and you have the money, definitely go for Landmark.
Do not compare Adelphi Suites in Bangkok with Adelphi Suites in Pattaya. Adelphi Suites in Pattaya is hardly a 3-star hotel. I would consider it a 2-star hotel. I was there once and considered that I made a booking blunder. Book a room in Adelphi Suites in Pattaya ONLY IF you are on a tight budget.