Air Asia is quite safe and usually much cheaper than the competition (even after all the fees are added in), but they do have a distressing tendency to have seriously (>10h) delayed flights. I gather this isn't nearly as bad as it used to be, though, thanks to their ever-expanding fleet.
That said, you can't fly Air Asia from SIN to DPS. However, Valuair (JetStar) does fly that route, and they're quite possibly the best LCC in Asia -- new planes, reliable service, good seating and even free food.