There's a few threads here on this topic; worth searching for them.
I have used both NLP and SmartConvert quite extensively. My current conversion software of choice is ColorPerfect, which is a Photoshop plugin.
I've used NLP a lot and even purchased the upgrade to the latest version. A couple of things caused me to move on from it:
- the conversions were all over the place, even with all the new "roll analysis" features, etc. Too often it was doing quite extreme corrections or plain weird things to the color. Caveat, I am feeding it raw files from a film scanner, not "camera scanning".
- and as the previous poster mention, it would often clip and lose data
- I really tired of the workflow. Having to access it's dedicated control panel to make changes, keeping two copies of files (the raws, and the positives)... all of that stuff became a pain in the butt for me.
SmartConvert I wanted to love. I really enjoy the interface, the keyboard shortcuts... the "lab scanner" workflow. I could commit to a conversion and have one file in my library that I would edit further in Lightroom. I went so far as to buy this as well. However, after a while, I realized that SmartConvert was almost always clipping highlights and adding an unnecessary amount of contrast. The deal breaker for me is that there's no way to actually avoid this; there's no histogram of any kind in the app. I emailed the manufacturer asking if they had any plans to add a histogram-- no response.
Enter ColorPerfect. Firstly, it has a terrible UI, and requires that I also run Photoshop. However, the conversions are consistent, and all I ever do with it is run the conversion and make sure I am not clipping anything and losing data. This is what I really like about ColorPerfect-- it tells me
exactly how much data is being clipped. I am able to do some minor color tweaks to fix any egregious color casts, then export a nice flat file and bring into Lightroom where I do 95% of the color correction. And I can be confident I didn't lose any data along the way, which, to me, since I want to edit using Lightroom, is the most important part. So in the end I have that one file in my library that has all the data from the scanner and frankly is pretty consistently at a good starting point as far as color inversions go.
My 3c!