Best way to store app settings that are configurable from administrator interface?
There's CraueConfigBundle that adds a controller and a service giving access to a list of settings. It seems like it's tightly coupled to Doctrine ORM though: https://github.com/craue/CraueConfigBundle
IMHO, you have two options, 1) store it in file (i think better to store this in parameters.yml, than config files); But in this case, after each settings change, you'll need to clean cache;
2) store it in DB. If you'll have any performance issues using doctrine, you always have possibility to update getter/setter to cache results in memcache for example.
p.s. Both ways have own pluses. I prefer to split applications settings from its configuration options. So if admin wants to change global app settings, maybe it's ok to edit parametes.yml ?