Stayed at both in July and both are very nice hotels and recommendable. I think the Conrad is a bit more sophisticated in some details, e.g. the wine selection at the EL or the afternoon tea also including wine and beer. But definitely nothing to complain about in the Hilton. It also depends a little bit about your plans. If you want to go shopping, I guess the Hilton is better located. In contrast, if you want to enjoy Marina Bay, the Conrad is ideal.