My feelings on Hella units are well known. Even when new, they're not good. They simply do not compare to modern reflectors for accuracy and maximising light output, no matter what bulbs you fit. I tried just about every type of bulb in stock units over 12 months including (as Martin mentions), trying the bulbs in different positions and whilst some were considerably brighter, I wasn't really happy with any of them. They lacked focus and allow spurious light where its not really wanted. Moving to modern computer-designed light units completely solved it for me and I still only use standard halogen bulbs. Considering they're only around £40 a pair brand new, its a no-brainer. I think Hellas cost that EACH.
These are round headlights with stock bulbs. All I did was upgrade power feed to headlights, added relays and dumped the Hellas:
https://www.youtube.com/watch?v=cEIkGpC72GY" onclick="window.open(this.href);return false; If you pause close to beginning, you'll see the headlight units. The reflector is the lens rather than the glass. They pass MOT every year and I can spot a wandering bunny for a quarter of a mile. I can also get replacement bulbs anywhere at low cost. My MOT tester was really helpful and verified the beam pattern was exceptionally good.
If you have square lights, you are somewhat limited, but Osram silverstar bulbs are a good choice, and you may find LED bulbs work for you (they didn't for me), but as I say, the reflectors themselves are very old-school and far more suited to tungsten or halogen anyway.
My recommendation is set aside the issue of bulbs for now and consider the bigger picture. LED bulbs are a very white light but from all the experiments I did, their range is less than halogen bulbs, at least in stock Hella units.
To my mind, trying to compensate for poor lights with whiter or brighter bulbs is like chasing your tail. It still leaves the underlying fundamental cause - lack of volts and/or crappy headlight units, only now you have the added problem of being reliant on a bulb that is less readily available than what you had to start with. Better to deal with the cause.