I've been a JRiver user for more than 10 years. It's rock solid and stable and I make extensive use of DSP (8 channels with X-overs and EQ). It only shows 1-2% CPU usage. Its WDM driver is a real strength enabling the routing of any external content through the DSP - in my case primarily Qobuz. Output from my turntable can be routed through JRiver with no problem. VST plugins are easy to install and work well. I've built the required X-overs and DSP for my speakers in Acourate and used JRiver's convolver with no problem either. The CPU load is higher, but everything works fine. As an experiment I've also tried full room correction (FIR filters for the 8 channels and upsampling) without any glitches. I can use REW and route it through JRiver to measure the transfer function of my DSP settings. JRiver doesn't have graphing capability which is a weakness and there seems to be no intention to develop it, either, which is a shame.
As a long time Qobuz subscriber I was recently offered a 90 day trial of Roon. After reading a lot of positive reviews of Roon maybe my expectations were too high, but I didn't subscribe. I didn't find the playing now screen particularly impressive with some text way too small and yet large amounts of wasted screen space. I use a large screen TV and the amount of blank space looked strange. Images of musicians/bands were often poor or non-existent. I generally liked Roon Radio - in fact its ability to choose music that I liked based on the seed music was also its downfall - it regularly choose music (from Qobuz) that I already had. Integration with Qobuz was excellent, but I much prefer the playing now layout of the Qobuz desktop app to Roon's layout. Qobuz' desktop app has improved dramatically over the last year - it used to be very buggy and was one of the reasons I wanted to evaluate its integration with Roon.
Roon's DSP was easy to implement. The graphs are good, but more detail would make them even more useful. I couldn't find a way to successfully measure the transfer function of my DSP settings in Roon - there seemed to be a lot of processing going on causing too much latency. My biggest dislike in Roon DSP is that to turn a particular filter off you only have to click in the vicinity of the appropriate button. This makes it way too easy to make a mistake and inadvertently send a full range signal through your tweeters. In JRiver you have to click inside a check box, which may look old-fashioned, but makes for much more precision and less chance of a mistake.
Overall, I just found JRiver more versatile, with numerous options for control -
mini wireless backlit keyboard and mouse (my favourite), several apps for tablets, phone etc.