I find this a rather stupid question. Anyone can tell you kamadan is the best place to sell things of all kinds. Yes you can sell in lion's arch or gtob too or even shing jea during some events, but overall kamadan will always be the biggest market.
Yes you can try to sell here on guru too, but why would you choose one over the other? just do both. Put a thread up here and spam in kamadan, one doesn't prevent the other.