In the interest of full disclosure - I've been a Dish sub since 2003 and have dealt with the various issues of all their DVRs. I've been enjoying my ViP 622 for the last 2-3 years and it's been generally very stable with less than 2-3 reboots a year. (Note stability and performance greatly improved when I added a APC 500VA battery back-up)
Spending the weekend with the wife and her family at my sis-in-law's apartment. She can only get DirectTV with line-of-site from her patio. She has a HR22-100 DVR connected to a Panasonic 720P plasma. I've noticed the thing is SLOW. Everything lags including channel changes. I went into the setup and saw there is a native pass-through option to enable output from 480i all the way through 1080p depending on source material. While it's nice to allow your TV or AVR/video processor device handle scaling, I think the mode switches add to the delay factor.
In comparison, my Dish ViP 622 is lightning fast! The difference in responsiveness is amazing.
As far as picture quality goes, I can't compare since my Panny TV is different, no A/B, different program material, etc. I suspect Dish and DirectTV are roughly equal with some advantages on some channels for each service. I'll say that DirectTV's DVR had the internet-timer setting feature far before Dish and I suspect it's still a more robust implementation than Dish's which I've found to be unreliable and touchy.
Just wanted to post a review since responsiveness/speed is something you deal with every interaction with the DVR (vs PQ which varies greatly depending on source material) and this may help some folks decide between the services, if you have the choice. I do believe both DBS are far superior to cable when it comes to pricing, flexibility and DVR quality.