I don't know if there is a "best" way to decompose features. In the User Story practice (which is not part of Scrum), there is a concept called "themes" that allows you to relate many stories to one or more "themes". For more on that topic, see: http://www.scrumcrazy.com/User+Stor...and+Themes
I've also heard of some organizations mapping as follows:
Feature has one or more themes
Theme has one or more stories
There is no "best" way to do it, IMO. This area is something that Scrum does not really define, other than to say that all requirements are listed in the Product Backlog. You could have features, themes, stories, acceptance tests, or even bugs on a Product Backlog as a Product Backlog Item.