With labels and components if you want to select a group of them you need to use issue search. If you are using epics you can use issue search as well, but you also get built-in functionality in JIRA Agile.
In the backlog view of a JIRA Agile board you have an Epic tab. This tab allows you to select the issues associated with individual epics. Plus it has functionality that makes it simple to add new issues to an epic. The final advantage is that the epic name is displayed brightly coloured alongside the issues in the list. This can be very useful when viewing the backlog and getting a feel for what work is coming up next.
You can see more about epics on the Atlassian Working with Epics page.
Components are useful for the technical team as they can span across many epics. A typical component might be ‘database’ or ‘UI’. JIRA offers the option to assign work for a particular component to a particular JIRA user. For example, all issues created with a component of ‘database’ could be assigned to Jill Smith.
Labels are much more adaptable and they have the advantage of allowing multiple assignments (so more than one label can be associated with an issue). With labels it is very much up to you how you use them.