Which Content-Transfer-Encoding when sending emails via C# or there are not any difference?

Question

I am sending emails via C# the way below

MailMessage mail = new MailMessage();
mail.To.Add(txtTestEmail.Text);
mail.From = new MailAddress("noreply@monstermmorpg.com", "MonsterMMORPG");
mail.Subject = "Test email from MonsterMMORPG";
mail.Body = "This is test email sent from MonsterMMORPG";
mail.IsBodyHtml = true;
mail.SubjectEncoding = System.Text.Encoding.UTF8;
mail.BodyEncoding = System.Text.Encoding.UTF8;
SmtpClient smtp = new SmtpClient();
smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
smtp.UseDefaultCredentials = true;
smtp.Host = "127.0.0.1";
smtp.Port = 25;
smtp.Send(mail);

It is default base64 i suppose. But i wonder which Content-Transfer-Encoding is best for sending emails via using windows server 2008 r2 default smtp server.

Are there any difference between different Content-Transfer-Encodings . Thank you.