*Swoons* The marble male really is incredibly stunning--I'm extremely jealous right now lol. Are you pretty set on pairing him with the blue female? I'd be interested in seeing pics of the copper female you were planning on earlier or any other females you'd consider.
Assuming you have a successful spawn, is there a certain amount of time you typically wait before attempting the next one? If so, would you make an exception under certain circumstances?
Since you've had such negative experiences in the past with your attempts to breed HM males, its seems like a successful pairing with one would go a long way as far as giving you more confidence and positive outlook for future HM male pairings, and as cheesy as it sounds, that alone could end up making a real difference. Because of that, part of me wants to say you should go with the proven pair since they're obviously your best bet for a good HM male spawning, regardless of which pair is "better" or more attractive.
Idk, hard call, I can definitely see why you're having a tough time deciding!