Hi, I have attended wedding dinner @Orchard Hotel previously and the ambience is excellent. Their grand ballroom have high ceilings and it is very spacious. One of the nicest ballrooms I have seen in Singapore, including some other good ones will be Novotel Clarke Quay, Concorde Hotel, Furama Riverfront, Grand Waterfront Corpthorne, Fairmont Singapore etc. The service in Orchard Hotel is good, foodwise is fine, just that it is not too accessible. Need a little bit of walking distance to the nearest MRT.
FYI, Orchard Hotel has an excellent chinese restaurant called Hua Ting, a very famous one with several culinary awards. You can find out more info about Hua Ting in the internet. Their main chefs will be the official cooks and caterer for the whole dinner event. This info was provided by my bf's sis because she has recently just confirmed her wedding dinner with Orchard Hotel 2 weeks ago. And she is pleased with their service and overall experience. Hope this helps. Thanks!