I use "common all garden" bulbs, nothing expensive or flash.
The only thing I may have done differently to other owners is:
While checking the radiator in the summer with the front bumper removed.
I inserted 2 pence sized penny washers about 1.5 mm thick behind the bottom brackets of the headlight units... Then the beam has been raised slightly... Obviously I have adjusted the beam manually to meet MOT requirements with a beam tester. My auto adjustment switch is on it's lowest height where before it was on maximum height previously.
Illumination is very adequate indeed.
One thing I will add though that I suppose many wont think about... Suspension upgrades and lowering the car ride height...
-35mm can equate to a drop in overall beam pattern illumination distance by 10 meters... The lower the headlights are in comparison to the road will naturally reduce the visual distance.
Why do you think LGV's and Sprinter vans etc. have such good illumination compared to cars...? Their ride height and headlight assemblies are much higher up.
Maybe that's why some 156 owners complain and others don't.... The difference between Veloce and Lusso models perhaps?
Food for thought.