Third; Halogen lights - In my opinion the best of the lights. Easily seen in the daylight, and due to the curvature of the reflectors, easily seen from almost any angle. In relation to strobe lights, which produces a very intense, but very brief flash, halogen lights build in intensity to the bright part of the flash, and then decrease in intensity. The beam moving back and forth across other objects, buildings, etc., also increases it's visibility.
This only applies to rotating halogen lights. As you said, rotating lights produce a brief but intense flash, which is good for shorter-range all-around visibility, but this isn't very effective for long-distance warning during the daytime. Stationary flashing halogen lights make up for that. If sufficient wattage is used - 28 or 35 is normal for smaller lights, but a bigger 50-watt light is ideal - stationary halogen lights are capable of warning motorists a mile away or more, even in direct sunlight. However, they aren't as good as strobes for short-range warning like getting people's attention in their peripheral vision at an intersection. With an appropriate flash pattern, LEDs can serve the same function as either a halogen flasher or a strobe, just not both - a large, bright LED light with slow, simple single-flash is just as good as a halogen flasher for long range, and a smaller one with a quick flash pattern lights up an intersection about as well as a strobe.
Rotating and flashing halogen lights tend to be the lowest-cost option for warning lights and provide excellent warning for the cost, but they do have some drawbacks. They require more maintenance: bulbs don't last as long as strobe tubes and power supplies or LEDs, but they are inexpensive and simple to replace, and the motors and gears can wear out and break over time. They also draw more current than strobes or LEDs, with a lightbar for a police car usually drawing somewhere between 15 and 30 amps, but possibly much more for the huge ones on fire trucks that have more rotators in them. Halogen lightbars are also usually taller than strobe or LED lightbars, leading to potentially worse fuel economy. But even with these drawbacks, halogen lightbars were the industry standard up until about ten years ago when LEDs began to replace them, and for good reason - they get people's attention, and you get a lot of light for not a lot of money.
Rotating LED lights are similar in effect if they actually use moving parts, but solid-state LEDs that simulate a rotating pattern generally produce a less intense flash, but the flash lasts a little longer to compensate. I haven't seen one myself yet so I can't vouch for it, but Whelen's new Rota-Beam R316 beacon appears to be a promising example of this. LED beacons that usually flash the entire beacon all at once but include "rotating" flash patterns, such as the Whelen L31, may be attractive, but this produces a warning signal that is significantly less visible, in all conditions, so for maximum effect, a flash pattern should be used that flashes the entire beacon as a single unit.
