We use Vudu and like it a lot. We converted our DVD library to digital and then combined it with our BIL to utilize that platform. Vudu is owned by Fandango so they are backed by NBC and Warner. They should have some sticking power as well.We’re big into the Apple ecosystem so use it. We have probably 125 movies purchased through it as the kids have grown (6 and 11). Personally I don’t like rewatching movies so don’t buy for myself, but would stick with Apple if I did.
Only thing that really matters is what company will likely be around in the future and I consider Apple at the top of the list compared to Vudu, Redbox, etc.
In reality, though, I haven't purchased a new movie in a long time. We have a fairly substantial library in case we want to re-watch something, but there's so much new content and so little free time to watch something as it is. Once we got our daughter past that "rewatch Frozen a billion times" stage, I don't have a huge need for purchased movies.