If you are working in the dark, its good to have some sort of general lighting to find your stuff. The under hood lights or utility lights are good.
If you are working under the hood on a bright day, in a dimly lit garage, or working under the car, a head light should be your first purchase. These things are amazing. Make sure you get the models with the 3AAA batteries in the light, not the battery packs in the back. That way, you can rest your head on the creeper while you are working on your back.
Next, I would get the smallest brightest puck lights you can get like those shown above. Look for strong magnets and COB technology. You want at least 2 of these. One faces down, the other should shine from the opposite direction. Reason being, the brightest hood lights/drop lights don't do jack when your hand, arm, or head creates a shadow. You want light flooding in from multiple angles and that means the little lights are going to be more helpful. And the little units can be placed closest to the work.
I have 3 Blue Point ECFPTHP4 and 2 Snap on ECFHKY. They are excellent, but were expensive even at the sale prices I paid. There are many like this on the market now (like those above, EZ Red models etc).
When you choose a puck light, get one with a REALLY strong magnet. When people test these, they stick them to perfectly flat surfaces, like the side of a tool box. But none of my cars have any flat sheet metal. You need a strong magnet so it will stick to a curved surface. And strong magnets are expensive.
Cordless COB lights are definitely the way to go.
