Your mileage may vary since not all Comcast headends are equal, especially after a series of Adelphia and Mom & Pop cable outfits, although this disparity is much less these days. The same does for quality (assume we're talking HD quality since nobody watches SD these days)...some areas overload their QAM channels and the stat-mux combined with variable bit stream encoders (such as Cherry Picker) deliver a picture that's less than impressive - looks like that nasty Dish HD. Most areas do a credible job of balancing 3 HD per QAM and the picture quality is slightly better than Dish. A few areas still on send 2 HD per QAM and it looks excellent. Overall Comcast delivers the better picture quality but, as I mentioned, your mileage may vary.
Price. Comcast wins hands down when it comes to bundling TV, Internet and Phone, which makes the overall cost of video service cheaper than Dish. That too will vary by your area based on whether U-Verse or FiOS competing in your area and, to be honest, your personality. My parents are sweet people and pay full price for their Comcast services. They get some slight discounts since they've been customers for 25+ years, but it's expensive. Me? I'm a demanding sod and a cheap wanker. I pay full price for nothing. My Comcast has been $119.00 for all the english speaking channels, sports package (Versus, Redzone, Big Ten), premium channels (HBO, Max, Startz, Showtime, etc.)...everything minus the foreign language and nudie channels...and 50 Mb Internet (currently). I have been paying this promotion price for many years. Why? Because I asked for it and I'm a demanding bloke. I have no problem calling the corporate office in Philly when I'm unhappy with service. Of course, your mileage may vary.
Video On Demand. Comcast wins hands down - no contest! Although I have one mediocre Comcast DVR (promotional freebie, of course) I pretty much use two Tivo Premieres. They are every bit as good as the Dish DVRs (especially since they were found guilty of stealing Tivo software and paid them one-half a billion to license the stolen technology) and I now have an XFinity VOD app on my Premieres, which works great! Oh, and XFinity TV (online and mobile video solution) also blows Dish-Sling and their TV Anywhere out of the water. Of course, I rarely lose it because what kind of a loser has time to watch TV on a cell phone or tablet when they should be working, spending time with family, or watching TV on their 60-80" HDTV?
Internet and Phone. Again, Dish offers nothing other than overpriced, watered down TV to the rural masses who have few other alternatives. Most of these people who are into a quality TV experience will select DirecTV. Comcast or FiOS (if available) are probably your best choices, DirecTV is likely your 2nd best choice, and Dish your last choice. Again, your mileage may vary but if you may also consider a Tivo and installing a good antenna. Finally, Comcast quality, service and reliability has drastically improved over the past five years. They had to because of FiOS and U-Verse.
