The FIRST Lounge in SIN is smaller than the Business lounge and far more enjoyable for it. Don't just think that the small food offering they have on the right as you walk in is all they have, ask one of the members of staff for a hot dish from the kitchen (Sweet and Sour etc..), also if you are lucky they walk around and offer a mean chicken tikka.

Showers in the First Lounge are nicer (IMHO) but the Business lounge usually has hot slices of pizza on offer and about a dozen computers with free internet access.

Overall, First lounge because you can, but give the business lounge a try as well. Hope that helps !!