Like I said, there are some differences in the installation process between the Hellwig and Hotchkis bars, and you should check to see what suits your needs and abilities.
As far as function once the bar is actually mounted on the car the differences are going to be relatively minor. The Hotchkis bar allows for wider tires compared to the standard Hellwig bar for the 67-72 cars (5906), but there’s “pro touring” Hellwig bar that solves that issue (55917). And all of that is moot if your front tires are going to be narrower than a 245mm tread width.
The biggest difference is that the Hellwig #5906 and #6907 bars are solid, and the Hotchkis bars are hollow. The diameter of the Hotchkis bars are larger, but because they’re hollow the spring rate isn’t massively different (probably a little stiffer). Obviously the Hellwig bars will be a little heavier, but if this is a street car we’re talking about it’s not big deal.
Also, the Hellwig #55917 pro touring front sway bar is hollow, although still a little smaller in diameter than the Hotchkis front bar. So the Hotchkis front bar is still probably a little stiffer, but neither Hellwig or Hotchkis publish the interior diameter or wall thickness of the bars so there’s no way to be absolutely sure without testing them both.
The Hotchkis installation requires welding, while the Hellwig installation can be done without welding (although it’s better if you can weld some of the mounts).
But since we have no idea how your car is set up or what your intended use of the car is it’s hard to say if one will be better for you than the other. On a street car the differences on the road are not going to be huge, and it will totally depend on what you’re running for tires and torsion bars.