I mean, there is an opening that let's you buy the supply on T4. I am going to go ahead and call that the best one there is. Or at least a contender. Probably could be countered by militia or something, though.
What opening is that?
Refer to CelestialChameleon's puzzle.
But I don't think that works for the question at hand, since it involves a lot more than just the opening. You need to specify most (maybe all) of the kingdom cards, so it's not very generalizable.
My counterpoint would be that all of these 'ideal openings' specify at least a few (2 or 3 cards, maybe 1 or 2 events) things themselves. I am only ever so slightly pushing this concept into 'determine all cards, the entire black market deck and shuffle luck'. A difference in degree, really. 
Yeah, but I think the degree is important. If you're laying out out the entire kingdom, then you're no longer providing the "best opening" but just analysing a specific kingdom.
Another way to put it is that I think the "best opening" should only be concerned with the opening. So in this case, the opening is Nomad Camp/Watchtower/Hamlet. We know that this is killer for one very specific scenario, but how is it in general, where the other 7 cards are unspecified and your luck isn't guaranteed to be perfect? I'd guess that it is not so great.
Exactly how crazy do we want things to go? Specifying just 2.5 cards and having free reign on events gets me a lot of craziness.
Opening with:
T1: Save (anything)
T2: Baker/Borrow: Tfair, Quest (gain Gold), Alms (Develop)
T3: Dev (trash Gold, gain Kc/power $5)
You can literally gain all cards by the end of T5 with
worst possible shuffle luck on the right board. Even without going that far, you can manage some pretty insane things without having to rely on low odds shuffles. Dumping 12 cards of opponent Junk (Kc/Mountebank), buying a $15 Doc (Kc/Bom/Death cart), drawing deck & Inheriting a cantrip or picking up multiple engine components (Margrave, Council room, etc.), drawing deck and trashing an Estate (Kc/Stables).
There are also a lot of setups where this is insanely powerful without a different $7 - Gov/Forge; Hparty/Expand, and maybe even Venture/Bank on a colony board.
In terms of a simple opening, I think the the best might be something like Hermit x3/Madman:
T1: Summon Hermit
T2: Trash Hov, Gain Herm, trash Herm; Alms for a Herm
When you want to mass Hermits, it is normally an excruciatingly powerful combo (MarketSquare, but also Csmith, Goons w/o other villages, Hop & a cheap way to get them, Secret chamber & +buys, Artificer) that poor players would never manage and be dominating when it is worth it to tank your deck to win the Hermit (Madman) split.
In terms of versatility something like
T1: Expedition (Use Baker coin)
T2: Mint, Tfair, Alms (Remake)
This gives you a 5 card hand with a power TfB. You get to Kc/$4 in 2 turns or you can just pound treasures & BM starting on T4.
