I've gotten used to the headstock location as 'best' --- is there a better one?
In my honest opinion, the heel is a better place. And I'll tell you why...
1) While the original heel adjust was/is one of the STUPIDEST designs ever foisted upon us bassists (having to remove the neck and/or pickguard), there are very simple tweaks that have come along to make it better - a channel and the ability to adjust it with a hex wrench. So when done right, it's amazingly functional. No need to remove the neck, less chance of screwing up a tool or truss nut (when done right).
2) With the heel adjust area, you can spread the strings out to turn the wrench, very easily. The string tension is relatively low in that area and you can leave the bass tuned to pitch.
The same can't be said with the headstock adjustment. The short area between the nut and either the tuners or string retainer setup leaves strings in that area very tight. Typically, adjusting the rod there will kink and/or gouge the strings, even if you detune them, which kind of messes with the neck adjustment process as it is.
That is, assuming you don't have a super long wrench for this, which is not common. But even with that as an option, you run into...
3) Removing wood from that area is definitely not the best move for headstock strength. Volute or not, unless you're supporting that with something stronger than wood, it's making that area weaker, no matter how you slice it.
Removing wood from a heel area is no issue either because that is typically the fattest part of the neck AND it's only job is to bolt to the body (or set neck or neck through to the body).
So yeah, if I have my druthers, it's heel all the way.
Honestly, the MM style heel adjuster wheel is one of the best ideas ever come up with for this. You don't even need a specific tool! Use an allen wrench... or a drill bit... or some other stiff object that fits it, then make an adjustment with no issues.
If there were dual-action truss rods out there with that wheel as an option, that is what I'd use in builds every time. It's easy, elegant, safe, modern, the best idea in practical design for that application.