Timing chains are usually considered better because they're more durable than belts and are intended to last the lifespan of the car. That said, they do go wrong, and can cause a lot of damage if they fail. Most manufacturers now fit timing belts, which need replacing every five years or so (depending on model and mileage). Prices vary but you're usually looking at around £350 to change a cambelt. Dealers will usually be able to tell you what's fitted to the car, otherwise a Google search should help.