Another case of using the wrong word. Both the belt and the chain are reliable. Durability is what you're really looking at. That is, the chain is more durable. I'm sure the chain would last 2 or 3 times as long as a belt. The only reason I can think of to use a belt is there is very slightly less friction loss so it's slightly more efficient. Chains need plastic slipper guides to keep them from flapping around and making noise. You give up a little efficiency to help with engine noise.