Sql Server 2008 to R2 Restore Backup from R2
Most likely the first one "MSSQLSERVER".  Thats the default name for a new installation.  The express one is the free version and limits your DB size to 10GB.  The 3rd one isn't an instance, just shared components so ignore that one.

You should verify by logging into the server from SSMS and typing in SELECT @@SERVERNAME first to verify.  If it only returns the server name, then the MSSQLSERVER is the right instance.  If it returns ServerName\Express then you're on the express edition.