Entity Framework 6 (code first) entity versioning and auditing

I have used the 2nd approach you mention, by overloading the dbContext SaveChanges() method:

public class MyContext : DbContext
{

 public int SaveChanges(int userId)
 {
    // Get all Added/Deleted/Modified entities (not Unmodified or Detached)
    foreach (var ent in this.ChangeTracker.Entries().Where(p => p.State ==  EntityState.Added 
    || p.State == EntityState.Deleted || p.State == EntityState.Modified))
    {

        foreach (AuditLog x in GetAuditRecordsForChange(ent, userId))
        {
            this.AuditLogs.Add(x);
        }
    }
    return base.SaveChanges();
  }
...

So if I want to log a particular entity, I just call the overloaded SaveChanges & pass in a UserId:

public void Update(StockCatalogueItem entity, int userId)
{
     _context.SaveChanges(userId);
}

I also have a custom DoNotLog attribute which I use to decorate the entity properties that I don't want to log. Without this, the logging could generate a huge amount of data, as each entity modification equals one db entry.

[DoNotLog]
public int CreatedBy { get; set; }

The GetAuditRecordsForChange method does the checking for any DoNotLog properties and returns a List<AuditLog> which gets saved in the AuditLogs table:

public class AuditLog
    {
        public int Id { get; set; }
        public int CreatedBy { get; set; }
        public DateTime CreatedOn { get; set; }
        public AuditEventType EventType { get; set; }
        public string TableName { get; set; }
        public int EntityId { get; set; }
        public string ColumnName { get; set; }
        public string Controller { get; set; }
        public string Action { get; set; }
        public string IPAddress { get; set; }
        public string OriginalValue { get; set; }
        public string NewValue { get; set; }
    }