All of the above! There are people who are SUPER specific -- they collect only a single series (say, Buffalo Nickels from 1913-1938), some people who only collect a very specific type within a series (Buffalo Nickels from San Francisco in MS65 or better), and generalists who just like anything that's pretty or interesting or gold or silver or from their hometown, etc.

There are 1001 ways to collect and it's fun to meet all the different folks and learn about their different approaches.