As far as I'm concerned, the reason to go first/business is the extra room. I couldn't care less about in flight "entertainment" most of which is not entertaining. If I wanted to see a movie, I'd stay home and rent one. So, yeah, I vote for the worst first/business seat over the best economy seat. There is sometimes the same amount of legroom in domestic first and in some of the exit rows BUT there is never the same amount of elbow room.
Poster "gre" gets it right. The shared armrest and the silent battle of the elbows because everyone thinks I, as a small person, should not get my share of the armrest, makes any coach seat pretty miserable, even if there is legroom.
The worst first class would just be a bigger seat, plus perhaps better food and drink service, and first on and off. The best economy class would instead have personal in flight entertainment, although it may also have a good amount of legroom. Which would be preferred depends on whom you ask.