Some people might think “If you’ve seen one superb deep cameo proof Jefferson nickel, you’ve seen them all.” Rather than specialize in one series these folks generalize. They attempt to collect one of each type of coin ever minted in the United States.
The goal of many type collectors is to find a nice example of each type. Since they are only getting one example they can choose the most common date. This allows one to buy a higher grade coin than would be possible if attempting a matching year and date set.
Attempting to collect a really complete type set can be a daunting task. Some early types are very expensive in any grade. Gold coins are never cheap. There are well over 100 types listed in the Red Book.
To make the task easier you can stick to types from the 20’Th Century. You can just go for the major types. Many folks skip the gold or just collect types made from copper, silver or nickel.
Of course there are those who want to do everything the hard way. They may seek out only the first year of issue for each type. Or maybe they go for only key dates.
PCGS and NGC have many different type sets in their Registry programs. You can browse their web sites and see what other people are collecting.
Collecting type sets is just one of many different ways that you can collect coins.