digital movie code redeeming questions

[bri4jenn]

I have some general digital movie code redeeming questions

Is it better to redeem a digital movie code on a retailer site like iTunes or Vudu or MoviesAnywhere. What is one of the retailers shut down or what if MoviesAnywhere shuts down.

for HD code redeeming
1) if the movie is 4k in iTunes, Movies Anywhere, and Vudu, is it better to redeem the code in iTunes
2) does iTunes still upgrade movies to UHD 4k if redeeming a HD code?

for UHD code redeeming
2) If the movie is UHD in iTunes, Movies Anywhere, and Vudu what is the best place to redeem a code?