The SQ lounge in HKG is fine - comfortable and good food selection. Unlike the others though, it has no natural daylight and is totally enclosed - close to where you come through security and close to the gates SQ use. If you are flying SQ it makes sense to use it and I've used it at times it has been quiet when I've been flying with other airlines. Of UA and TG, I prefer TG, something about the food offering and the staff I prefer.