pulling best match from textfile search

Hello
the code below will pull a matched word from a text file and display the line it matched something on. It will even display 3 lines that matched the same word.

but what I really want to do is to take the line with the most matches so if textbox1.text was entered "How would I learn c sharp the fastest" than it would take the whole sentence into account and then display the most accurate line with the most matches from the text file.

private void button1_Click(object sender, EventArgs e)
        {
            int counter = 0; string line;
            StringBuilder sb = new StringBuilder();

            // Read the file and display it line by line.              
            using (System.IO.StreamReader file = new System.IO.StreamReader("C:\\TextFile1.txt"))
            {
                while ((line = file.ReadLine()) != null)
                {
                    if (line.Contains(textBox1.Text))
                    {
                        // append the text and a newline into the StringBuilder buffer       
                        sb.AppendLine(line.ToString());
                    }
                }
            }
            textBox2.Text = sb.ToString();
        }
   }
}