Text vs HTML: what is more secure?

There are "good" mailing lists and "not so good" mailing lists from the point of view of security.

Try posting HTML mail to a "good" and one of two things will happen.

1. If you have a mailer that includes the plain text then the list
   software will discard that, forward the plain text to the list
   with a message reading

   [Non-text portions of this message have been removed]

   I'm sure you've seen that message in posts on yahoogroups and similar.

2. If you have a mailer that doesn't include the plain text
   then one of two things may happen:
   1. The plain text version is displayed, but being null the text that appears is
      empty, but you still get

      [Non-text portions of this message have been removed]

      I'm sure you've seen that too.

   2. The list software does its best to convert the html to plain text by stripping
      off the html tags. This works, but may
      produce some odd results. However you still get

      [Non-text portions of this message have been removed]