I had Dish for 2 weeks (a 722 and a 222 serving 4 TV's), and I found their setup to be obnoxious..
First thing to remember, with Dish, you don't have MRV, you have 'TV2 out'. TV2 out uses the second tuner in the DVR to drive a TV in SD. So while yes, you could jerry rig it into a 'whole home' type system with a couple splitters, it isn't really MRV. Your TV2 is also at the mercy of the recording timers whether you can watch it or not. If you're watching TV2 and a recording timer goes off, you're either stuck watching what's about to record or you have to cancel the timer. And then there's the fact that there is no way to get TV2 in HD. If you want HD you need a separate box anyway. The only plus side to the system is that TV2 does get DVR features on live tv. But unless you live alone (and even then it's got potential to annoy you), it's a rotten system.
With Directv, you have a box at each TV, no matter how you slice it. This is a good thing for many reasons (and it costs the same or less than the Dish method of billing, depending on your setup). First, it keeps the DVR tuners free to do DVR things. A record timer doesn't interrupt anything. It also allows the MRV system to work (again independent of what is happening on other boxes - you're not interrupting anything), so any HD box can watch anything recorded on any DVR in the house. The only thing you don't get is DVR controls (live pause/rewind) on non-DVR TV's. There's also complaints that the Directv UI is ugly and dated (which I agree with), but dealing with it is a small price to pay for a better system. The unofficial official word is that the UI will be updated by year's end anyway, so... I have two HR24's, an H24, and an H21, and I don't have any responsiveness or sluggishness issues at all right now. There was an issue a while back but it seems to have been fixed in the current software.
Another thing to consider is how each company bills for extra boxes. Directv bills flat $6 for each additional box, regardless whether it is a DVR or standard. So if you want 4 DVR's, it's $18 total in box fees (plus the $10 DVR/MRV fee). Dish on the other hand bills by the tuner, and they charge extra for DVR's. A single tuner box is $7 (211), a dual tuner box is $14 (222), a regular DVR is $17 (622 or 722), and a Sling DVR (922) is $19. So if you want 4 DVRs with Dish, they nail you for $51 a month just in the box fees, on top of the $7 DVR service fee, which doesn't even have MRV.