I would reject both a trader association and a miner's association. The fact that the market is self regulating would make it difficult/impossible for an exchange without transparency and ethical operations. Having a miner's association would potentially open the network to 51% type attacks as the miners would literally be working together
Well, the exchanges now are all but transparent. Are they solvent? Are they front-running their clients? Are they faking orders and traffic? Do some clients have special privileges (like a few seconds advance knowledge of the order book)?
For a 51% attack, it suffices that the 3-4 largest miners collude. That is much easier backstage than through a professional association. On the other hand, a miner's association could better spot and sue fraudulent manufacturers, for example.