Comforters and bedspreads are generally sold in the same section of bed and bath specialty stores or any large department store. Both are designed to fully dress the top of your bed and cover up any of your linens, such as sheets or quilts. Both can be made from similar materials like cotton and look very similar in terms of shape and texture.
A comforter usually just covers the top mattress. It usually drops around 15 inches over your bed's edge and only fully covers the top. You might find that you can see the edges of the mattress. Many people who purchase comforters choose to add a bed skirt to cover any remaining parts of the bed and give it a more cohesive look. Comforters are often, but not always, filled with soft down.
A bedspread, however, will generally cover the entire bed. This includes the area from the pillow all the way down to the floor, or close to it. Bedspreads are typically not filled with down and are simply cotton or flat fabric.
As comforters are generally filled with down, they will appear light and fluffy. A bedspread resembles a very large blanket and is generally not as soft. Comforters are also usually reversible and have a similar or complementary design on the back. Bedspreads are not reversible and are often simply white or a solid color on the underside. Depending on the material, comforters are generally warmer than bedspreads.
Many people love the soft texture and reversibility of a comforter, but prefer the complete coverage a bedspread can offer. If you have a full-size bed, you could consider buying a king-size comforter and using it as your bedspread. The extra size will easily fit over your bed and hover closer to the floor. Just make sure to get something that isn't too fluffy and will easily drape over the sides of your bed. You can also put a plain white comforter under the bedspread for added comfort.