How do you plan to 'distribute' the offspring?
If there is a local breeder/seller, talk to them and see if there is something you could breed and supply them with. This will save you the step of advertising, shipping, etc...
If you are only interested in local distribution, then talk to local stores and see what sells and what they feel would work best...
If you wish to make a little business out of it and accept the burdens of advertising, taking orders, shipping, etc, etc... Then I suggest shopping around and seeing what the competition is lacking.
GT and low grade FH are readily available locally for most of us, so it's unlikely you'll find people eager to pay shipping prices for these...
I don't know enough about hybrids to know if you could realistically breed high grade FlowerHorns or what that would take. But buyers are likely going to want to see & buy half grown fish so breeding them will likely require more grow out space.
That leaves Midas, Devils and Festae...
I would shop around and see which of these three options I could get the absolute nicest breeding pair. If you just plan on buying 6 to get a pair... I think it would be silly to assume you are going to get a "high grade" pair that produce "high grade" offspring. Instead if you truly want to make a quality breeding pair I believe you will be shopping for above average young adult or adult specimen that are wild caught or close to it...
Start shopping and see whats available...