Heavier the denim =?
Heavier denim is usually a lot more durable and they take longer to stretch out. Someone correct me if I'm wrong but I don't think that denim weight has very much effect on the fades they produce. There are a lot of factors that go into how denim is spun, how indigo reacts to diff kinds of denim, wearer's lifestyle, etc.
I agree with everything above, except IME, heavier denim doesn't take any longer to stretch out than lighter denim, so long as their weave tensions are similar. Tighter-woven denim of any weight takes longer to stretch out, and stretches less, than looser-woven denim.
One thing that I do want to add is that heavier denim tends to be smoother, softer, and less slubby than lighter denim.