In my opinion and by way of comparison Dish Network is the best as far as the number of channels to the over all cost. They offer more movie channels (TMC extra, HBO Comedy, 5 Star Max, etc…), a few more basic channels, (though DTV does have some channels that Dish doesn't, but the numerical amount of channels is greater with Dish).
DN’s equipment is at least slightly below the level of DTV. Not in features though, DN has interactive capabilities on all of their new receivers, (at least they are supposed too) DTV only has it on select receivers, same for caller ID, amount of FAV lists DISH=4 DTV=1 etc... Though all receivers have bugs and such, after being a DTV customer for seven years, the biggest thing I had to get used to when I switched was REALLY buggy equipment.(everything from the program guide, video dropouts, etc…) Dish Network is also more complicated, where as DTV uses 101, 110, 119, (Though lately there is DTV satellites parked at different locations, they as of yet don't require customers to point a Dish to those other locations, same goes for DN's other locations.) Dish uses 61.5, 105, 110, 119, 121, and 148, and on top of that 105 and 121 require completely different LNBF's. Granted Dish is supposed to be working on getting rid of 61.5 and 148, they still make it complicated by dividing different programming among different satellite locations and by offering two different SuperDish setups.
Voom, the biggest problem with Voom in my mind is this; they don't have the basic channel line up that I would like to have. They do have the most HD, but I am not one of those people were HD is everything, and therefore that doesn't impress me. If you like HD and you don't care about all of the channels that they don't have then go with them. Or if you can afford to have DTV or Dish along with Voom, be my guest. Voom is also very expensive, both for equipment and programming. (Unless their $0 down promo is still going on, but even then they are still very $ on the programming side, and yes I understand you are paying for HD, but 90% of the HD that they offer I wouldn't even pay a penny for).
I was a DTV customer for seven years, and I've been a Dish customer for two years, and between the two, even with buggy hardware, I still like Dish better than I did DTV. I've looked at Voom and I don't like the line-up or the price so it is out of the question for me.
Hope this helps, in the end it will be your decision, all anyone can do is give you their experiences.