I do believe that the Corda is the best in it's price range. I say that without ever hearing the Creek, because when I talked to people that have heard both, the Creek didn't better the Corda and the Corda has the advantage of having crossfeed, variable no less. I did hear a MG Head with NOS tubes that I might have preferred and it's in the same price range. It's got the tube sound that I like but doesn't have the crossfeed and it's had some issues with quality, so the Corda would get the nod if only because of the crossfeed and reliability. However you can add the crossfeed fairly cheaply if you have some DIY skills.
I have a Headroom Maxed-out-home, and without crossfeed enabled on either unit I prefer the sound of the MOH, which I find more airy and transparent. However, the MOH is 3X the cost of the Corda, and I like the crossfeed in the Corda better and I always use crossfeed, so that's a vote for the Corda.
Unfortunately I have not heard the Headmaster. It's a all discrete design with no op amps with impecable build quality with the flexability of additional inputs. From what I've read it sounds like it's very transparent but maybe not as musical and relaxing as what I would want from an amp.
I just ordered a Berning microZOTL which I'll get in a few days. I have heard one before and was quite impressed. I would like to hear it against the Earmax Pro but that probably won't happen. I plan to use it with an external Corda type crossfeed circuit. From what I remember in comparison to the MOH it similar but more liquid and relaxed without giving up much detail and intensity. It's in the same price range as the Headmaster but I believe it will be more to my liking. Tubes do the sound differently than solid state, and I generally prefer the sound of tubes.
In summary, for me I think the competition with the Corda at that price is really a rolled MG Head with an external (or perhaps added internal) crossfeed circuit. You have to judge for yourself what sound you're after and what goes best with the rest of your equipment.