Only you can decide what your needs are. We are can't do that for you.
What are you looking for in your new nook, and what do you plan to use it for?
It really depends on your needs.
While each device has its issues, I found that the NOOK color and the NOOK tablet, when they just came out, worked pretty good for what they were intended to do.
From my own experiences with the Nook color and the Nook tablet, I would go as far that for pure stability, B&N does better with a brand-new device rather than having it get more stable over-time.
For both there were some updates that resulted in some complications, partially as the result from newly added functionality.
The NOOK HD was designed with the new services B&N is releasing in mind, and of course is used as their main testing device for those services. Some of that will of course port back to the NOOK tablet and maybe even the NOOK color, but B&N's main focus will be the new models.
I think the higher resolution on the new nook HD is a compelling feature. Text is going to be noticeably crisper, so I think that will be a significant benefit to its core function of reading. And, since it's running with a faster processor and a new version of Android underneath it should have noticeably smoother operation too. Not that the current nook tablet is a slouch in either of those areas, but the HD should be a significant step up.
If you can stand the little-under-a-month wait, I'd say the HD is worth it.
There's also the fact that the Nook HD is the newer technology of the two and will probably be supported longer. If things like that are important to you, that's something to consider as well.