About the JW Marriott. The rooms are much smaller than the Conrad's. I stayed as a Marriott Gold and had lounge access. The offerings were good at breakfast, tea and cocktails.Unfortunately, unlike the Conrad, I couldn't have breakfast at the restaurant (well I could but I think it was something like 27 Singapore dollars each). I like the location of the Conrad better. It has closer access (I think) to the Esplanade that often has interesting things going on at night. I frankly would not pay for lounge access at the Conrad. Last time I was there, the offerings were sparse and blah. Breakfast at Oscar's is terrific. Both have good access to the MRT.
I walk around at night, but I find it too hot and humid to walk very far in the day time. I will walk to Marina Bay Sands from the Conrad in the evening, but I take the MRT to the Gardens in the day time.