I am using Comcast as my primary provider now and I must say that even on the 3:1 mux channels, quality is no worse than Dish. The On Demand service negates any missing HD movie channels for me and the DVR has the ability to record to my pc over firewire. Quality on the 2:1 muxed channels will destroy anything on Dish. I've tried watching TBS and TNT side by side with Dish and Comcast, since I get both with each provider, and the resolution and encoding differences are glaringly obvious. The Comcast channel looks better. Dish seems to recompress everything to the same washed out color-banding prone standard that looks a little washed out and blurred on a larger screen. Plus, your local channels will look better on cable since they will 99% of the time be exactly the same quality as the OTA feed. I'm not trying to nudge you in any direction, but quality is not an issue and various reports from AVS Forum and others have found that the 3:1 muxed channels are much better than they were when they were first implemented and are now almost indistinguishable from the source.
If you are satisfied with Dish quality, which I was not, there are advantages to staying such as the DVR capacity. On the 722k the storage is twice that of the largest cable box. 500GB versus 250GB. That does not include something like a TiVo. Plus, with MPEG4 compression that Dish uses you can fit many more hours on the hard drive that you couldn't with cable even with the same size of hard drive.
When I went back to cable, my main concerns were quality and channels that I wanted that Dish will likely never get or won't get until a few years from now. Those include MLB Network, ESPNU HD and my RSN in HD full time. You should compare what is available in your area and see if that compares favorably to Dish. That is especially important if you get HD because the lineup can vary greatly by where you live with cable. The quality issue is subjective to each person, but I know full well that a 17 megabit average MPEG2 channel is going to look better than a 3-5 megabit MPEG4 channel. And it does. The 3:1 muxes leave room for about a 12 megabit average per channel. In MPEG2 terms, the quality on those at their worst is at least going to be comparable to Dish HD which uses low bitrates for MPEG4. It was really not a hard decision for me. You should compare them first though if you know anyone with cable and see how it looks to your eyes.
A big disadvantage to cable which had me ready to dump them again and switch to DirecTV is that utility work can disrupt your signal and there is nothing you can do about it. I am now thankful for my ordeal with DirecTV that involved them using my father as the reason I couldn't get their service even though we don't share a name or a residence and he hasn't had their service in five years and I'm over 220 miles away from him. Since the utility work has ended I have been given a credit for the time that my service wasn't the greatest and I'm happy with what I get. That includes internet speeds up to 50 megabits now.
The bottom line is that if you are satisfied with what you have and what you pay then you should keep it. dish's Absolute HD is a great deal in my opinion.