Standards stipulate that the preferred segment of a multipart/alternative message, which this is, is the last of those available alternatives which the user interface comprehends.¹ The last such component here is text/plain.

If your interface doesn't offer you that portion, then ask for "view page source," or some equivalent, braindamaged nonsense.

I have placed text/plain last, as being the most correct display method for what I have to say.

¹ RFC 2046, MIME Part Two: Media Types, §5.1.4, pp.24-25:

   ...Systems should choose the "best" type based on the
   local environment and references, in some cases even through user
   interaction...
   ...In general, the
   best choice is the LAST part of a type supported by the recipient
   system's local environment.