The 18 oz. shaker is used to cap a 28 oz. shaker much like the 16oz. The main difference is that the 18oz shaker sits higher inside the 28oz to allow for more liquid content inside the shaker. The 18oz shaker is still small enough to be used as a cheater tin. This shaker has a reinforced bottom, which is also known among flair bartenders as a weighted shaker. Same high quality stainless steel.
Deciding on the ideal shaker tin is purely subjective, and you will become comfortable with any type you choose. If your interest is clean ease of use, a 3-piece shaker may be your solution. For working bar workers who are looking for quickness, a two piece system of capping a smaller tin or mixing glass is common, as is preferring instead a single tin for mixing and an ice strainer to separate the ice. 2-piece shakers are also offered as a set, and so often look is a large consideration. If you're looking for a bit of color and no slip grip, you may want to try the vinyl-coated shaker. Picking stainless steel or plastic is a factor when purchasing limits and show of both professionals and home bar enthusiasts are important.