There are a few things to look for when buying a light bar for a truck. Aside from the obvious (what size you want and what your budget is), there are a some other factors to consider.
1. Shape Of The Truck
One thing that lots of people fail to consider is the body of the truck. Most of today's trucks have a very sleek, aerodynamic body, with lots of soft curves. Older trucks, like older, 1980s Chevy Silverados, have boxier, straighter lines. This means that if you do not buy the right bar, the aesthetics of the truck will look off. We, and most other off-roaders, recommend that you get a light bar shape that fits your truck, and for most that will be a curved light bar.
2. Truck Usage
If you aren't an avid off-roader, or don't go truck camping much, you might not need an expensive light bar, or even need a light bar at all. If you were just looking for a little extra light on poorly lit highways or side streets, you would do better with LED flood lights or spot lights. But if you do like to go off-roading, especially at night, a full sized LED light bar is what you would need.
3. Mounts and Brackets
Mounts are specifically made for each model of truck, and not all models have mounts for them for each light bar. If you were looking for mounts, so you don't have to drill the brackets directly into your roof, you need to double check and make sure the mounts you have are compatible.
4. Light Bar Quality
Far too many people don't think twice about spending $1500 on mud tires for their Wrangler, but then try to find the cheapest light bar they can. This often times turns out to be a mistake, for several reasons. Cheap light bars (like the ones you find on eBay) are often constructed poorly, and can fall apart after only a few years. You can even feel the sub-par quality of the parts when you hold them. They also do not protect against water/dust as well as a more expensive one; poor construction means moisture gets trapped in the housing, degrading the electrical components. The LEDS these cheaper manufacturers use are also very misleading. Cheaper light bars will use "over charged" LEDS; that is, because the LEDS are made using cheaper materials, they are not as bright as more expensive ones. To give the illusion of quality LEDS, the maker will often run a current though them that is more than the recommended; while this gives the illusion of more light, it also means that the LEDS burn out far quicker. So make sure to only buy light bars that use American made CREE LEDs, and that the light bars have an IP protection rating of 67, which offers protection in all but the most extreme circumstances.
So What Is The Best Light Bar For A Truck?
The all around best light bar for a truck is the 50 inch 5D curved light bar. It is long enough to fit almost any truck, and the curved shape helps to fit with the rest of the body. The downside is that it doesn't come with any mounts, so drilling into the roof is required.