I used to use MPC-HC for foolproof playback with ffdshow and EVR, and JRiver for tagging and organising my media. Then RedOctober HQ happened at JRiver and I said goodbye to ffdshow for good.
I also found that JRiver's DSP settings for surround upmixing (JRSS) were better than Dolby IIx to my ears. So in one of my home theatres, I upmix 5.1 to 7.1 using JRSS and then add height or wide channels in my receiver for 9.1 (using Audessey DSX) that sounds very good. This will finally be 11.1 in a couple of weeks when my new Onkyo arrives.
JRiver has a lot more to offer than a typical directshow player. I still use MPC-HC as a backup. Since I'm a Beta tester of JRiver, the latest build very occasionally introduces a problem, and it's good to have MPC-HC to tease out whether this is a problem with the file, the hardware or the software. Conversely, since JRiver installs and sets up LAV and MadVR, it's a great diagnostic tool too for those with codec problems.
In another thread where someone was having image quality problems with VLC, I recommended JRiver to test out. If there were an improvement I suggested that he either buy the software or learn how to configure MPC-HC to achieve the same results for free. I think I'd give JRiver the edge for ease of configuration of advanced features like auto refresh rate and resolution switching, audio settings and reclock-like video smoothing. Not to mention the improvements being made all the time by the excellent staff. Overall I'm quite satisfied with JRiver, and I am quite sure that my setup is only using about 25% of its potential. After 5 years, i still learn about new (old) features every weeks.