Jonathon,
I have and use all four of the apps you are considering. I have been a big fan of PhotoKit Sharpener from the start, and think it does a great job. It has good control for localized sharpening, and provides for a good variety of output requirements, plus it lets you paint in the sharpening as you need it. All good stuff. In comparison, Nik Software's Sharpener Pro is actually much easier to use, in my opinion, and does an outstanding job with its default settings, but you can still tweak things. I think its Display sharpening for Web use is very nice, and something I found harder to get done correctly with PhotoKit. I also like the Sharpener Pro settings for various paper types in the Inkjet sharpening, and the fact that it does sharpen things based on the size of the output. You can see the differences in levels of sharpening for an 8x10 versus a 16x20 for example. Not a "one size fits all" approach. I also like that you can create the sharpening in a layer and further set the opacity of that layer, as well as paint in the areas on a mask for more selective control.
On the sharpening front, Nik Software's Sharpener Pro has been winning in my book. My only issue is that I would like to see them update the plug-in to work properly with Mac OS X 10.5 (Leopard) on Intel machines running CS3. Presently, it does not work there, and requires PS CS3 to run in Rosetta, which is dog slow and a waste. I keep my G5 running on Tiger (10.4) just for the better performance of some things like this app. If you are on a PC, that may not matter, but if on a Mac, it is worth considering.
On the noise reduction front, Noise Ninja has been my favorite since it was released, and I recently got the new plug-in for Aperture, which is blazingly fast. I think the NN controls are good, but still feel that it tends to be a bit aggressive and wipes out a bit more detail than I care for at times. For "busy" images, this may not be an issue, but it can impart a bit more of a "plasticy, too smooth" look too quickly if not used carefully. You can build profiles for various file types and save those. The defaults are supposed to be camera specific, but I have found that forcing the app to profile the image gets better results over using the camera defaults.
After picking up Nik Software Dfine, my preferences are again starting to change. I think Dfine has a much less harsh noise reduction algorithm, and it works on each image with a profile, rather than camera presets/defaults. It also has nice control over edge contrast and edge sharpness, better than similar controls in Noise Ninja, in my opinion. It can also be used selectively on a layer mask, and also offers quite a variety of presets to deal with specific things, such as noise in sky, or just working on skin tones. I find this can work nicely, and quickly to create a nice skin softening, or to clean up sky and background without hammering the main subject. Overall, I find Dfine to be a bit more flexible and not as aggressive as Noise Ninja.
So, while all four are very good and useful apps, my preferences have started to swing more in favor of the Nik Software plug-ins over the Noise Ninja and PhotoKit Sharpener for how I use these tools. I still keep all of them loaded, and I do use some for different things, but my first choices are now the Nik tools over the others. They may not be the fastest, and they do create a layer (which can be flattened) in PS, thus making for a larger file, but I feel they offer more overall control to the user in a variety of ways.
As I said, I just wish Nik would get Sharpener Pro updated to work on Mac Leopard properly, AND to get both Dfine and Sharpener Pro done as plug-ins for Aperture. I think that will happen at some point.
Not sure it my comments help. I think it is worth downloading and testing them yourself, as all can be downloaded for demo, I believe. They have different approaches and the UI is a bit strange for each, but you can quickly get the hang of it.
LJ
