Simply put, high quality HID projectors are the best way to go. Most bolt-on projector headlights lack a good beam spread. With factory halogen bulbs in them, they're worse that your OEM headlights, and with HID bulbs in them, they're barely any better.
If you want to go with the easier option and get the drop-in projectors, get yourself some quality bulbs. Morimoto actually started making halogen replacements in sizes that fit most projectors, and they're not too expensive ($40/pair). Note that they don't offer colors higher than 6000K. That's because going over that severely decreases the amount of light output. Stay away from the $40 kits you see on ebay. The bulbs are very poor quality, with less than adequit halid salts in them (where the light comes from). You typically get flickering, and most of the time get hotter running bulbs that don't last very long.