If you spend time in direct response circles, the matra is A.B.T. - always be testing.
An addendum to that might read "ABV" - always be valuing (visitor value, that is).
I've personally tested both. It really depends on how html vs. text affects:
a) your open rates
b) your clickthrough rates
c) your sales conversion rates
d) your long term lifetime value and visitor value.
It's very dangerous to make decisions about "html vs. text" based upon one's own personal preference - or even HN readers (unless that's your target audience).
What do you know about your audience? That's what I always say when chatting with friends and colleagues.
As an example, are the majority of your users using gmail, hotmail, yahoo, aol?
Or, are they using personal and/or academic addresses?
These different mailing providers treat html vs text quite differently.
The style of your email can affect whether or not you get inboxed (hence every action step from open rates, to ctr rates to sales will be affected).
What's the demo of your audience? If one has an older crowd, perhaps plain text may be easier to read.
A younger crowd? Perhaps xyz percentage more of them are reading via mobile devices. This would also affect the decision.
The Email Experience Council at the DMA has some great research on this topic - check their Youtube channel.
But above all I'm a big fan of making data-driven decisions based on a clear awareness of what your audience's behavior suggests - not on personal preferences or HN likes - IHMO.
Also HTML may be more appealing but text may drive more goal conversions.
Has anyone else seen better overall ROI with text, even though they personally have more of a preference for HTML?
added:
http://www.emailexperience.org/
http://www.youtube.com/user/EmailExperience