The only person I know who has experience with both sells Cibie. The big difference between them is build quality and materials. The Lightforce lights are light weight plastic while the Cibies are very well made, somewhat heavy metal and glass. The Lightforce lights allow you to control the size of the cone of light with a zoomable reflector, and to some degree with protective filters. The Cibies have a very well made, precisely ground glass lens. What this means is that the Cibies control the light dispersion more, but they are what they are. With the Lightforce you can control the general spread of light, but not things like cutoff.
While the description makes the Lightforce sound comparatively cheaply made, it really is just a different way to make a light. The Cibies, being heavy, require a stronger mounting. The enclosures can handle heat from high wattage bulbs very well, but you are more likely to crack the lens on a water crossing (hot glass, cold water). The Cibies have a replaceable lens reflector if you crack one.
Do a search for Cibie and Lightforce lights on the Australian expedition forums (exploroz is a good one) as there is a pretty good sample of both lights in use there.
I've always been happy with Cibie lights, but I don't have much to compare them too.
