Pippin Williamson has written a good explanation of which to use over on Wptuts+.
TL;DR: If the functionality is something that should continue to work after you switch themes, then it belongs in a plugin.
Pippin Williamson has written a good explanation of which to use over on Wptuts+.
TL;DR: If the functionality is something that should continue to work after you switch themes, then it belongs in a plugin.