teriyaki

So combining a few Amex promotions, i'm looking at a one-time opportunity to punch well above my regular hotel budget for one night in Singapore. We'll be flying back after a week in Thailand, and have one night layover with 2 full days before and after check-in/out.
I would normally never stay in hotels in this price range, but with the AMEX Fine Hotels and Resorts program i've found that the benefits bring some of these properties to a level I can actually start to justify.

So the hotels that qualify (all within the same price range) are:

Shangri-La
Four Seasons
Mandarin Oriental
St.Regis (for a little more).

The Fine Hotels program provides a $100 dining credit to use, so wondering if any of these hotels have a restaurant that must not be missed. I would normally be eating at hawker stands, but with this opportunity I'd really like to get some others inputs on which property likely has the best food.
Other important factors are, ease of access to MRT for airport. Ease of access to activities outside of hotel after check-out.

tvhead

I have to suggest that you look at Royal Plaza on Scotts. The rooms are not quite in the same quality class. But the breakfast buffet is tremendous
If you stay there, you can splurge and book into a 'Club' room. But go to the buffet for breakfast, it's much better than the more modest club offering.
And the location gives you great access to MRT, and lots of eating choices around the hotel as well.

number_6

I like the Shangri-la but not sure any of these hotels work well with your criteria. Another choice is Swissotel/Fairmont (they are two towers in the same hotel complex, and both owned by the same company now, which is Accor). Some excellent restaurants at both of these hotels, including Jaan which has 1 Michelin star (but USD 100 food credit wont get you a meal there, more like 300 minimum for dinner). Worth getting a harbour view club room.

dsgtc0408

Going by the OP's list of hotels, the situation is a mixed bag. There isn't one clear standout, especially when food is concerned. But as far as food goes here's two links from a random Google search:

12 Best luxury hotel restaurants in Singapore

https://sethlui.com/best-buffets-singapore/

To be clear I don't vouch for any of the restaurants stated here but I've put up these links so the OP can have some idea what choices are out there. I'm like the OP, I eat a lot at hawker centers, not fine dining. Having said that note the Mandarin Oriental houses Morton's Steakhouse which is always good and always pricey. number_6 is correct in saying that a $100 credit won't get you far, thus the listing of hotel buffets.

In terms of where to stay in order to maximize access to the MRT and chances to do stuff, it probably would be either the Four Seasons or the St. Regis. Both of these are just outside the core Orchard Road shopping belt - a ten minute walk to the MRT. In fact both the St. Regis and the Four Seasons are around the corner from the last/first stop of bus 36 (front of Regent Hotel), which goes to Changi Airport via mainly highways aside from going down Orchard Road and a detour through a residential area in Singapore's east. It's a good alternative considering there's going up and down escalators in the MRT, there's the need to change two trains to get to the airport (to be fair both train changes are just walking across a platform) and the travel time is just a bit longer on the bus due to traffic.

On the hotels I wouldn't consider: The Shangri-La is in the general area of Orchard Road but is a ten to fifteen minute walk past a lot of residential apartment buildings to get to the St Regis, and then another ten minutes to the MRT. It's really quiet there. The Mandarin Oriental is a dark horse choice because its location is in a part of Marina Bay where it's quiet-ish, and getting to the MRT is somewhat convoluted.

SanDiego1K

You will find a lot of good information in this thread from the Luxury Hotel forum.

Best Luxury Hotel in Singapore? (consolidated thread)