Choosing a reg to rebuild depends a little on what your final goal is. If you plan to add a Phoenix or MK3 then look for a DA Aquamaster. A Royal AM will also work but they tend to sell for a good bit more and considering the parts that you will replace in the conversion are the same ones that differentiate a DAAM from a RAM, why pay more if you are going to remove the parts anyway. Same goes for round label regs (later models) vs square label models (earlier models) the only difference is a slight design change in the outer shell (aka- can), internally they are identical. On the other hand, if you intend to keep it original, then the extra cost of a RAM may be worth it. Similar models of Voits are also good choices but they are harder to find and usually sell for a lot more due to them being more collectable, again, same internals with slightly different outer cans.
How the regs perform underwater has a lot to do with can and hose design, the place where the new Mistral fails or at least that is what I have heard from those who have dove both
Granted this is second hand info but from folks I know that should know. I really need to dive one, that is going on my to do list this summer. Before making a decision, why not get Karl to let you test drive a restored DH reg so you can compare for yourself.