The answer to your question depends upon what you want to watch and on how often you want to watch it.
If you just want to watch an occasional big sporting event, then 24 hours of access to all Sky Sports channels for £6.99 might be better than paying for a monthly satellite subscription package. But if you're a big sports fan then paying over £200 per month to watch sport every day via a Now TV box is clearly not a good idea.
Similarly £8.99 per month for unlimited access to 800 movies might seem a good deal but there might not be that many films that you actually want to watch. Netflix, at just £5.99 per month, might offer more content that you like, whereas Sky TV has lots of movie channels available if you sign up to a suitable package. However if you want the best selection of movies (particularly recent releases), Blinkbox's pay-per-film system might be better for you.
There are similar arguments for and against a Now TV box with regard to the general entertainment channels. For example, the only 'non-Freeview' channel that I'd really like access to is Gold. It would be ridiculously expensive for me to sign up to Sky in order just to get that one channel. However I can get it for £4.99 per month with a Now TV box (which I might well consider doing). But someone who wants to have LOTS of entertainment channels available would probably find the NOW TV selection very limited, so they might be better off with Sky.