I like a variety of image development software, especially when it's free. DXO have just released DXO Optics Pro 9 elite version as a free download with Digitial Camera UK. Sign up for it here:
Why use DXO Optics pro?
When I've used it, the software has given my images a more subtle, less gaudy look than I find instinctive with Lightroom, but also with great sharpness. There's nothing to choose between the capabilities of Lightroom and DXO, but their default settings are different, and the way the sliders work tends to push development in different directions.
Why not use DXO Optics Pro?
Version 8 (that I still have on this computer) was very slow to import folders and build previews, even when accessing the images on a SSD. Also images exported from DXO as DNG and TIFF format files displayed with different tonality in Lightroom when I imported them from the way they looked in DXO. I could deal with that OK and had a correction preset prepared, but my Nikon D610 camera (acquired a year ago now) was too new for version 8, and that killed it for me. However the D610 IS compatible with V9, so I'll probably re-start using it.
Since I'm talking about developing images, there's a couple of things worth mentioning.
Using the Nikon has changed my approach, though not my workflow, when processing images. While image sizes are only a little larger (24 vs 20Mpx) the RAW files are 50% larger, presumably containing more data or with less compression. This means that I can push images a little harder without seeing artifacts from processing, and particularly, means that I see benefits from increased sharpening - anything up to 120 units vs 75 max units for the Sony - is usable. This is partly down to the larger file sizes and possibly also down to the relatively low sharpness/contrast of lower spec Nikon glass. I've never failed to be disappointed by Nikon lenses compared to Sony/Minolta, and while sharp images can be had, it's not something that I can rely on.
The Nikon files themselves don't lend themselves to the bright, punchy images that came naturally from the Sony, which is a double-edged sword. It has reigned back an inclination to 'wind it up to 11' with the sliders, but does mean that if I want bright and punchy, it's easy to end up with something that look bad, rather than looking just a bit too bright.
On-one Photo suite is still used, though less these days because the Nikon files don't always respond as well as those from the Sony, though layers can still be useful.The best features in effects are still dynamic contrast, glow, colour enhancer and the vignette tool. The mono conversions are also good, and are very effective as a *digital* mono tool.
Nik Silver Efex is my main mono conversion tool. As with everything its strengths are its great 'film-like' mono conversion quality and powerful tools (that don't always have as much precision as the maker suggests) to re-shape an image. Its weakness is that when pushed too hard for the image it causes really bad halos and can easily be over-used. I did fiddle with the rest of the tools in the suit, but TBH they offered no advantage over anything I already have while still having the halo problem.