I imagine AU is the overall better option. SG is a city state, AU a seriously huge country. More options, can live in town, or countryside, or jungle or desert, close to the beach, or close to the skiresort. Higher quality of life, less stress. and not confined to pigeon hole HBD. Also a bit more free and open society.

I think the pro's for Singapore would be all about the proximity and cultural similarity to Malaysia.