First post and you are asking for favorite headlamps. OK, I will play. Mine is the Zebralight H501. I like it because:
1. It's small, so small I can carry it in my shirt pocket or on the belt at all times, even when I sleep. This is important because I adhere to the "The only useful tool is the one you have with you when you need it" principle. Say you are in a high-rise that's on fire. The lights go out. It's dark and difficult to see. You need a headlamp for hand-free use to see and help others. Whatever your favorite headlamp, it doesn't do you any good if don't have it with you at that moment.
2. It's versatile. Most headlamps are just that -- headlamp and nothing else. Because the H501 is so small, it can be removed from the headband and turned it into a flashlight, desk lamp, shirt light, belt light, lanyard light, overhead light, etc.
Until someone makes the perfect headlamp (which I doubt), the are always trade-offs. For my use and need, the small size and versatility of the H501 outweigh any trade-off.