There are many different types of lights out there, but with saving money in mind over a period of time LED lights are the way to go. And with recent technology advances Led lights are WAY more affordable than they once were as some of you may know.
You can get pot lights that will fit into a junction box where your old out dated lights used to be! The only down side to these ones is that they protrude from the ceiling about 3/4" which some of you may not like. If you have an attic above the fixtures that you are looking to update it is much better and possibly easier to remove the old junction box and install your new slim LED pot-lights instead, and of course they do not protrude from the ceiling and provide a much better broad light as they are flush with the ceiling. These pot-lights are available in 3",4",5",and 6" with different brightness's you should look out for when purchasing these lights! Also another thing you should consider is sticking to the name brands (yes I know they can be a bit more expensive but the quality of the light and the product is what you are paying for and it is so worth it.