Light is light. If its 4300k hid or a 4300k halogen its the same light. It doesnt reflect off stuff differently or anything else. Hids use less power, make less heat and last longer. You wont find halogen lighting at sporting events in large stadiums either....
If you cant afford hids then a good halogen is a good choice. But if your willing to spend the money. Hids are what you buy.
As for the reason the new model vehicles with factory hids have auto leveling its because hids are so much BRIGHTER than the old halogens that the cheaper bottom end non luxed out cars they make for the masses that cant afford the higher end nice lighting have.
The old halogen lights have a far worse problem with vertical unwanted light polution than the hids. But they are so dim in comparison to a quality hid kit that no one cares if the bounderies have bleed over, because they dont bother people.
Hids hurt when you get them in your face. The auto leveling on the factory vehicles solve this somewhat. They still have the same problem that shows up when the person in front of you is actually lower than your vehicle but your on level ground. Also they have a limit on how far they can auto adjust so you can wind up blinding people with the factory ones too.
A quality hid kit has a very pronounced light cut off that halogens lack. If you aim them responsibly you wont get flashed and you wont bother people that much. But face it when you put a gazillion candle power on the front of a vehicle its still going to be painfully bright even if the headlights are aimed directly at the ground.
Try putting some kc daylighters on the front of your truck and running them as headlights. They are halogens just a ton brighter than anything available for normal headlights. Your going to be supporting those statetroopers for years to come.
As for the hi/low issue. There isnt one with any of the high quality hid kits. They are high and low beam lights. The bulb itself shifts in the housing to change from low to high. This actual has an advantage over dual element halogens as they turn off for a second going from high to low or vice versa. One element goes off and the other element comes on. Hids with high/low just move the bulb. No flash, no gap in lighting. Just smooth transition as the bulb changes from high to low.
Hids are far more shock resistant than halogen bulbs, last far longer and use less power. Even a 55watt hid system onces energized only pulls 35watts or less normally. So thats 70 watts total power consumption or load on your electrical system. An 80w/100w halogen pulls a full 100watts on highbeam. Thats 200watts total power when your driving down the road at night.
So the halogens are using 130watts more power than the hids system. Thats 130watts you no longer have available to power your wipers, a/c, fan and other electrical needs in a bad storm.
If your alternator goes out at night you can drive farther on a hid based system than you can a halogen system.
The hids should be better on your headlight housings and cause them to yellow less. Not exactly sure on this but it sounds good
Anyway Im a hid fan as anyone could tell from the above post. If there was something I thought was better than the hids for headlights Id buy it. I havent seen anything that touches them in my opinion. Ive run piaa, silvania, hella, ge, and a few others. I couldnt find anything I remotely liked.
Now I will admit I doubt I'll upgrade my bmw. Its running halogen bulbs and it does pretty good but it has a vastly superior headlight housing than anything available for our trucks. It would probably be even better with hids but I cant see changing them since they do all I want.