Depends what you're after. For some people the three things they're interested in are price, price and price, but others are interested in other things, such as reliability and quality of service.
Most utilities offer crap customer service these days and there are plenty of stories of broadband being unreliable, so if Demon are providing a reliable connection with decent service when you have a problem ... then that's what you're paying for, and you should consider whether you really want to move to a flaky connection with no service just because it's cheaper.