These are all important and have different functions as they are components in the Store Model Theory (also called Stage Model Theory) of human information processing theory. Context will play a part in how important or what priority each stage may have in a given situation.
Sensory memory accepts information from the external environment and begins processing it. Some would say this is the most important component because it begins the process. Keep in mind, however, that this is related to external (environment) information. You might want to do some research on sensory deprivation studies before attaching too much importance to this step in the process.
Short-term memory retains information while the brain is using it and for short periods afterwards, thus it's referred to as conscious memory. When the brain has no more use for it in the immediate moment, it "lets the information go," so to speak. This information can become forgotten or it can move to long-term memory, depending on its importance to the brain, some of the techniques the individual may use to try to retain it, and a host of other factors. Some of these other factors can include what type of and how much other information is coming in at the same time, the individual's emotional or physical state of being, what importance the individual attaches to the information.
Long-term memory, also called preconcious and unconscious memory, is the component of memory that retains information for later use. Preconscious information is relatively easy to recall. Unconscious memory is not available while conscious but may surface while dreaming, daydreaming, or otherwise not thinking about it.
There has been much research on how information moves from one stage to another and methods for improving long-term memory storage and recall. They key to your question, however, is that all three components play an important part in how the brain receives, stores, and recalls information.