Spizza at 29 Club Street was first recommended to me just about when I started work, but I've not gone a huge number of times, mostly because of its pricy nature. I think the standard for a basic meal there is about $20 per head...
Anyway, Spizza is pizza with a difference. The standard pizza in Singapore (Pizza Hut and Domino's) is a thick, cheesy kind of pizza, whereas Spizza serves a wickedly thin, generally un-cheesed pizza cooked in a traditional wood-fired-oven style. So you can really taste that Parma Ham. For additional flavour, every pizza combination they serve is named with a different female name starting with one of 25 letters of the alphabet (all except X).
Here's an example.
Overall? It's decent for a small gathering (if pricy), but you might run into some of these conflicts:
1) Your group doesn't enjoy this type of pizza
2) If they do, a small group of you won't be able to order all the pizzas you would like to taste over 1 gathering
3) The Club Street outlet doesn't sit large groups well. It's kind of a narrow space so you have to sit all in one row - which tends to limit conversation to within 1 table's reach (2 persons each direction).