There are a variety of different kinds of resins that can suit your needs. Some cure really fast, which I find are good for testing molds, but they are prone to having bubbles in them. Other resins take longer to cure, but it allows them more time for air bubbles to escape. Some cure white/opaque, and others are crystal clear.
So, depending on what your goal is, it's good to know what you want from your resin.