I didn't read all of the responses in here, but I have had all three. (Dish, Direct, and Comcast). What I have now is Dish Network. We had Comcast at first and they were just to expensive for TV, so we switched to Direct TV about a year ago. I wasn't really worried about HD when I switched to Direct nor when I had comcast. The reason I ended up switching was in fact because I now wanted HD and DVR. I initially called Comcast to check out the bundle for all three services that they had! The price looked pretty good, but then they added all of these extra charges as I started to actually go through and sign up, so i was just like forget it. So I called Direct TV (what I currently had) and was telling them that we had been a customer for a good while now and that we wanted to upgrade to HDDVR reciever and they said that they could give me one or the other but not both, if I wanted both I would have to pay $100. So then I called Dish Network and told them a lie. They asked me what I had and I told them that I had two HD DVR recievers and two regular boexs on non HD TV's and told them I wanted to get the hookup. For the first 6 months I paid $19.99 for two HD DVR recievers with there basic package and after the six months, went to $49.99 a month after the promotion was over, which was still less than $60 dollars I was paying to Direct TV and I got two HD DVR recievers and two rooms with Dish and I only had two SD boxes with Direct. I have been overall pleased with Dish Network, but it does go out a bit more than Direct did. I don't think I ever had a problem with Direct TV going out, but it's gone out like twice since I have had Direct (2 months or so), but it is just for a few seconds and then it comes back on, nothing major or a long amount of time.
If you have the extra money to spend I would stay with Comcast or go to Direct TV, you won't have any issues with either one of them as far as TV goes except for price. If you are wanting to stay on the cheap side and get pretty good service, free install, and all the free recivers that you want (at signup) then go to Dish and tell them that you are switching from Direct TV. They really do hook you up if your switching from one to the other.
Sports channels are going to be about the same. They probably all have most of the same packages. However, I'm not sure if Dish and Direct have the "SEC Media Channel" which is going to be like WFLI or something I think. So I would make sure that one of them have it and do what you want.
Just my two cents. I honestly haven't had a problem with any of them except for price.
Also one thing to note that I had forgotten about is that Direct TV now has a thing called Score Guide that is really cool and I really miss it switching from them. You basically hit a button on your remote and it brings up a small menu and you choose whatever sport you want to check out. It will show live scores and the cool thing is that it will show you what channel the game you are checking out is playing on. For example, it was baseball season when i discovered that they had it and I was wantin to watch a Braves game and so i click on Braves vs. Mets and it had like 3-4 different channels that it was being shown on. really comes in handy for sports!