It really is a matter of how fast is fast enough.
SCV is potentially the fastest service, but because cable modem users must share bandwidth, the throughput (data speeds) can drop at peak times.
ADSL, the technology used by SingNet Broadband and SingTel's Magix caps speeds at 512kpbps or 256kbps but you are 'guaranteed' of those speeds at all a times.
If you want a cheap, pretty reliable connection and already have cable tv, go with SCV.
But, if you want consistently good speeds, check out SingNet Broadband: http://www.singnet.com.sg/product/broadband/promotions.html
or SingTel Magix: http://www.singtelmagix.com.sg/product/product_features.asp
Just to confuse things further, Pacific Internet also offer an ADSL-based broadband connection: http://www2.pacfusion.com/sg/broadband/
Basically, PacNet and SingNet Broadband offer the same sort of service. Magix offers online movies and news on top of normal Internet services. SCV offers a cable service that's good enough for the average surfer.