Osram Night Breakers are my legal favourite bulbs. Osram Rally 65 Watt for the non EU compliant bulbs.
Ah! Will check handbook as didn't think I had HIDs - Handbooks notoriously complicated, easier to whip the bulb out & check - Thanks
This is assuming you don't have HIDs, which I would have thought an HSE would have.
HIDs i would again choose Osram as a first choice, Phillips as a second choice. HIDs also get dimmer with age, so it could be that they have simple aged.