Based on your earlier shortlist (Sofitel, Four Seasons, Kempinski), I’d suggest Kempinski. Sofitel is not the same league as the other two and I’d say is more of a 4* than true 5* hotel (it’s also in the business district, essentially on top of an MRT station, and surrounded by apartments and offices). The Four Seasons in Singapore I have found to be hit and miss (and the hotel itself is a mix of renovated parts and older parts, and I have to say my experience is that the rooms tend to have a musty smell) - crucially, a deluxe room in the FS will essentially overlook a large construction site, so you’d want a Boulevard room (pictures below if helpful). Kempinski has good rooms, good eateries, an excellent bar, and it’s very close to Raffles, Raffles City Mall, National Museum etc, but if I recall also has some construction next door (I think a Pullman hotel or similar is being built, so you probably wouldn’t want to face it).

Ritz Carlton - service wise, excellent bordering on hard to beat in Singapore, but the rooms are very dated and the windows lack any decent soundproofing, with rooms on the quieter Marina Bay side being closer to the lift shafts which you will hear all night if you have any sensitivity to noise. For those reasons, it’s overrated in my humble opinion.

Best luxury hotel in Singapore … Raffles. Best overall hotel, Conrad.