Storing values in the web.config - appSettings or configSection - which is more efficient?

I'm writing a page that can use a couple of different themes, and I'm going to store some information about each theme in the web.config.

Is it more efficient to create a new sectionGroup and store everything together, or just put everything in appSettings?

configSection solution

<configSections>
    <sectionGroup name="SchedulerPage">
        <section name="Providers" type="System.Configuration.NameValueSectionHandler"/>
        <section name="Themes" type="System.Configuration.NameValueSectionHandler"/>
    </sectionGroup>
</configSections>
<SchedulerPage>
    <Themes>
        <add key="PI" value="PISchedulerForm"/>
        <add key="UB" value="UBSchedulerForm"/>
    </Themes>
</SchedulerPage>

To access values in the configSection, I am using this code:

    NameValueCollection themes = ConfigurationManager.GetSection("SchedulerPage/Themes") as NameValueCollection;
    String SchedulerTheme = themes["UB"];

appSettings solution

<appSettings>
    <add key="PITheme" value="PISchedulerForm"/>
    <add key="UBTheme" value="UBSchedulerForm"/>
</appSettings>

To access values in appSettings, I am using this code

    String SchedulerTheme = ConfigurationManager.AppSettings["UBSchedulerForm"].ToString();

For more complex configuration setup, I would use a custom configuration section that clearly defines the roles of each section for example

<appMonitoring enabled="true" smtpServer="xxx">
  <alertRecipients>
    <add name="me" email="me@me.com"/>
  </alertRecipient>
</appMonitoring>

In your configuration class you can expose your properties with something like

public class MonitoringConfig : ConfigurationSection
{
  [ConfigurationProperty("smtp", IsRequired = true)]
  public string Smtp
  {
    get { return this["smtp"] as string; }
  }
  public static MonitoringConfig GetConfig()
  {
    return ConfigurationManager.GetSection("appMonitoring") as MonitoringConfig
  }
}

You can then access configuration properties in the following way from your code

string smtp = MonitoringConfig.GetConfig().Smtp;