Depends on the application:
LEDs and incandescents for idiot lights.
Incandescent, HID, LPS or linear fluorescent for area lighting depending on the specific requirements of the application.
Big incandescent lamps for pissing off green crazies.

Big incandescent lamps for pissing off green crazies.

That reason I like the most... :-D

MV for simplicity and durability.
LPS for its efficacy and visual acuity.
M-H for the science (contruction & operation), for usefulness as a growlight, and for the high CRI.
LED for its rapid expansion into everything including the bluest & brightest car headlights I've seen.

Bright,Blue car headlights-these MAY be LED.For the most part they are Xenon or Xenide.A miniature HID light.You find these in portable handheld battery powered lights,too.I have a collection of portable HID lights.Polarion is the king of these.HID car headlights come in other colors-5K,6K blue,and 4K white.You also see Green,pink,purple.These colors come from the halide salts in the arc tube.And amber color HID foglights-really just a miniature HPS lamp of sorts.BMW and some other carmakers have gone to laser lit headlights-when these shine towards you you see a "specular",dazzling,effects.And they are 4K in color.BMW uses these.And yes,LED headlights available too-Prius comes to mind.Mercedes uses them,too.

Bright,Blue car headlights-these MAY be LED.

As a lighting enthusiast and expert, I never walk, drive or bike without a diffraction grating in my pocket.

I can't stress enough that it's MUCH MUCH more difficult to figure anything out without one! LED spectra are quite distinct from HID halide-salts spectra.

Headlights have evolved faster than any other niche. I was shocked to see big semis on the highway with LED headlights, 2 YEARS AGO!

The LED headlights are rather a novelty than any technical advantage. Unless they are used with conjunction of some advanced adaptive beam technology - but anything more complex than a single gap (and that is available even with halogens with some car models) in the beam is still by far not yet in production (although approaching)...

By the way you may have noticed, how their proponents don't hesitate to stress how the lower power demand saves the fuel when they are in use. But "somehow" just "forget" to mention the extra mass the LED technology means to just be road worthy (beside a heat sink to cool the LED chips, it needs a headlight front lens heater to keep it transparent and not disturbing the light pattern - a "service" traditionally provided by the otherwise parasitic IR radiation from the incandescents or even HID's) and how that extra mass is responsible for way higher increase of the fuel consumption anytime that car is driven...

I like magnetic MV and preheat or mag. rapid start fluorescent.  I like 6500k fluorescent lighting too. Don't forget the warm glow of an incandescent bulb.

I like clear MVs or clear top lifeguards.

I forgot to mention also acid frosted incandescent bulbs.