Banquet may be the worst, but they sell them for 75 cents apiece at the market here. That's pretty hard to beat, but I only stick with the ones I know are good: the roast turkey+gravy, macaroni & cheese, and swedish meatballs. The rest is crap.
Now, as for the best, Hungry Man would be my pick but they have insanely high amounts of calories, fat, sodium, and cholesterol. I wouldn't recommend eating them every day, make it like a once-a-week treat or something. As for stuff you can eat every day and not die from it, Lean Cuisine's paninis are my favorite. The pizzas aren't bad either (mmm BBQ chicken style) but they tend to be a bit more unhealthy.
Oh, and some of the frozen Boston Market food is pretty good too, but not very health-conscious.