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I've read great things about the H4's. I currently am running Sylvania Silverstars, and found them to be much better than the OEM lights - fairly inexpensive, too. But they are glass and heavier than the original plastic lights.
The Sylvania SilverStars or the Hella conversion units are glass but they will not be an issue with the later C4 headlamp motors and gears.
SilverStars are probably the best bang for the buck; figure about $50 for the pair and it's a simple plug and play. The 6054 lamps should be available at just about any parts store.
The Hella conversion lamps are as easy to install but figure on $50 for each unit and then you need a good H4 bulb. The bulb that comes with the Hella lamp is (if IIRC) just a halogen bulb. There is a SilverStar H4 bulb and you can find some good Xenon H4 bulbs. These are higher wattage, but as long as you don't go above 80/100 watts, the factory wiring will work with no problems.
CIBIE also has a 6054 conversion lamp and they are good too. It might be harder to find Hellas and CIBIE's in stores.
I had Hellas in my 92 with Xenon bulbs and I really liked the beam pattern. The low beam has a sort of flat top to it and that helps prevent glare when driving in fog or heavy rain. The lens is cut to make this pattern and also directs extra light to the right side of the beam pattern to better light the side of the road.
I've got Hella H-4's now, and had Sylvania's Cool Blues. The Hellas 100-80 are super bright and have not burned up the wires yet. Have tried many combinations but the Hella H-4 are the best to date.
You can get Sylvania Halogen H0654 at Advanced Auto & others for about 9 dollars a piece or you can get the Sylvania Halogen H6054 "Cool Blue" for 17 dollars a piece. I am changing the headlights in my Vette today so, that is how I know. Last, the Cool Blue is not like the Euro lights you see in the luxury cars.