I think what it boils down to is that provided you don't have to be there for a specific time (concert/special event etc.) then Tiger are usually always the cheapest. I have been delayed both times I have used them but I have friends who come from Sydney and they have never been delayed - definitely luck of the draw on that one. I have to say being delayed wouldn't put me off flying with them again because they are so much cheaper and the service was excellent.
Also it is cheaper to book direct through the airline rather than say Webjet who charge a booking fee on top of the actual fare.
Hope this helps and you get sorted soon