I've been researching this subject this week because I'm interested in doing Exposure Fusion which is similar to HDR. If you want realistic, you want to use fusion instead of HDR. HDR requires a tone-mapping step and it's quite difficult to get natural and realistic out of it. Fusion bypasses tone-mapping and is superior for coming up with a realistic output, and doesn't add noise (actually reduces noise, some say) or create chromatic halos around stuff.

Photomatix is one of the few HDR packages that will do the fusion process. I don't own Photomatix Pro yet but I will by the end of the day so I can't speak from experience about the software's operation but here are some tips I've learned from numerous web sources:

1) Photomatix Pro sells for $99 retail but there are a number of photographer sites that give you a code to use at Photomatix to get 15% off - in other words a $15 discount. They then get a commission for having sent you to Photomatix with their code.

2) Photomatix Essentials or Pro works best if you convert your RAW files to TIFF (8-bit or 16-bit) using an Adobe product before putting them into Photomatix for processing. People have been complaining about blurry output created from files that were not blurry going in. The Adobe RAW converter in Lightroom or Photoshop is FAR superior to the one in Photomatix. That's not an opinion - Photomatix says so themselves in their FAQ section and THEY tell you to convert to TIFF in an Adobe product BEFORE doing HDR or fusion. I've never seen a software company tell you flat-out that part of their package is crappy and they know it. That's being pretty honest! Also, if theirs is crappy, the competitor's RAW converters are at least as crappy if not worse but they don't say so.

3) Photomatix now includes plug-in ability for LR4 and LR5 which solves that conversion problem and allows an efficient workflow. It also works with earlier LR versions but has some restrictions on LR1 and sometimes doesn't work right. This means you can convert your files to TIFF in LR, highlight a bracket group of TIFFs in LR, right click on one of the group to "export to Photomatix" and do your thing. The finished combination photo file is then imported right back into LR in the same directory, just like most other plug-ins do. Then you can touch up the finished file as you prefer it to look or even use other plug-ins on it from within LR. I like the idea of staying in one place for the whole process.

4) Photomatix is the standard of the industry (I suspect with more users than all their competitors combined). Their sample galleries by numerous international photographers will knock you out. After reading a ton of consumer reviews of other products and photographer blogs, I've learned that those products also have blurry output - likely caused by poor RAW converters in them but nobody has mentioned that concept that I've seen. Most HDR software packages are going to be selling for $50 to $100 so why not just buy the industry standard which is reportedly easy to use (I watched a couple YouTube videos about that), does everything that every other product does, and also does Exposure Fusion for more realistic output than HDR for $85?

5) Photomatix Pro also does simultaneous bulk processing of HDR or Fusion auto-bracket groupings to save you time instead of just doing one at a time. Essentials apparently doesn't do that.

I've been using Dynamic Photo HDR5 for the last 9 months (also blurry when using their RAW conversion). I'm moving over to Photomatix Pro today so I can start doing fusion when my 7-shot auto-bracketing camera arrives Wednesday!

I'm not sure I understand your question. Yes, Nik's programs are all plug-ins whereas Photomatix isn't. Functionally, however, I don't see much of a difference. One opens on its own; the other opens through Photoshop. Yep, that's the difference that I see.

My workflow--Bridge > CS5 > Nik Plug-ins > HDR Efex Pro 2 > CS5 > Lightroom > Printer--lends itself to using Nik.

I'm not saying, "This must be your workflow!" All I'm saying is that this works for me quite nicely. Here's an image that was developed using that workflow.

Its called HDR for a reason, Just submitted one of several processed versions of that shot. Some very natural, some more dramatic. The finished process is always reflective of the processor. UP-2-IT, it is not "chromatic aberration" it is called "tone mapping" it's done in the software not in the camera. If you understood HDR, you would have known that the 2nd shot was unprocessed, and just one of the downloaded required exposures. So no "fluffy clouds" needed. Use the UHH search option for HDR. You'll find it very informative.