OP, here's the short answer:
Ultimate solution: looking at what's important to you- 1) quality picture, 2) quality sound, 3) extras, 4) specific subtitles, I suggest you embrace 4K BD discs and roll your own to gain the convenience of on-demand digital (copy) playback too. You won't do better on the stuff you care about in that list than 4KBD (until there are 8KBDs).
And here's the long, long answer:
You're posting a question seeking
objective answers from a very
subjective crowd, akin to posting a question asking about republican ideals in a democrat-heavy forum or asking this group which OS is better: Windows or MacOS? By the time you have the last post in this thread, expect to have mostly Apple-centric recommendations. We are the crowd that can ridicule stuff like mobile payments and bigger-screen phones to no end while Apple doesn't have either for sale and then gush about the greatness of both as soon as Apple does.
Closer to this exact topic: look up ANY
TV thread for the last few years and you'll see an overwhelming amount of anti-4K sentiment that is increasingly quieting down lately as that crowd buys that God is about to roll out a 4K
TV (and they can't very well call God wrong for doing anything):
- NFC (mobile payments) is a "useless gimmick", etc until ApplePay is rolled out and then it's group sentiment about wanting to boycott stores that won't accept Apple pay(ments)
- Bigger-screen phones were abominations, fragmentation-driving, one-handed use, pants with bigger pockets, man-purses vs. the perfect size of 3.5"... and then the perfect size of 4"... until Apple rolled out bigger-screen sizes which then became the new "perfects" (and one hand everywhere apparently grew, and pants-makers found magical ways of making bigger pockets without them showing)
- 4KTV is a stupid/useless/gimmick that no one needs, "the chart", 99% can't see the difference, I cant see the difference (so you can't either), until the internet bandwidth is upgraded everywhere, file sizes, I don't want to throw out a perfectly good TV set, until everything in the iTunes store is available in 4K, etc NOW EVAPORATING as written sentiment as the rumors gain strength that Apple is actually going 4K with the little box.
So keep that in mind as answers keep coming in. In general WE are very, VERY biased to whatever Apple has for sale now, only shifting a bit close to big launches when rumors have sufficiently piled up that we start believing Apple is offering something else very soon. Once Apple rolls out the changes to what was, almost all the passionate arguments that ridiculed the changes evaporates and suddenly the very stuff we used to so robustly put down becomes prime reasons for "shut up and take my money." That written though, I am surprised that you've got a few responses that aren't just blatantly gushing Apple/iTunes already. Impressive.
To your issues:
"Extras" are not exactly offered in abundance in iTunes either. The capacity is there but the follow through is pretty severely lacking. They can definitely be found with some videos but many have nothing more than the main feature. If extras are very important to you, I'd encourage you to go the disc route and convert from disc to iTunes yourself. Just about every disc will have some-to-many extras, you'll actually own a copy of the video (on disc) and you can convert it with your own choice of quality settings rather than hoping some stranger in some corporation chooses a quality setting that pleases you. You'll also have a tangible backup for worst-case scenarios that can't be removed from your access because a Studio decides to pull it for any old reason. And it's there to convert again should some new format replace the one in use now (for example, what if h.265 is not limited to only 4K videos but Apple leaves <4K videos as h.264 for backward compatibility for at least a few more years? Roll your own and you can go all h.265 by your own choice). For abundant extras, nothing competes with the disc option.
"Subtitles" is the same. Go the disc route, download whatever subtitles you desire and roll your own. That will get the subtitles you desire the vast majority of the time. Else, you are hoping the stranger decides to include the subtitle language(s) you want. They may, but it may be like the extras inclusion too. Why leave it up to some stranger that can't even possibly know what you like/want and be exactly right?
As to "quality" of picture & sound, there is so much variability in that question that nobody is going to be able to give you a defacto answer. I suspect that it would vary even film to film unless both corporations are getting access to the exact same rendering. There would also be other factors like your own choice of television and other playback hardware, speakers, receiver/amplifier, etc.
Even if you took a crack at a scientific approach- maybe randomly sampling 20 videos available on both, objectively viewed (blind tested) each head to head in your own home on the exact same televisions & sound systems, etc and "A" was judged to have 12 out of 20 better looking and/or sounding videos than "B," I would not be so quick to assume that "A" generally provides better looking & sounding video for ALL videos.
If you did such a test on a much larger number- maybe 5% of ALL videos available on both services- you could probably make a general blanket statement about one delivering higher quality picture and/or sound than the other at that point in time. But allow a little time to pass and the loser can adapt per those findings. Example: Apple Marketing spun Homepod mostly only "higher quality speaker." If that turns out to be true, how hard is it for the competitors to put different speakers in new versions of their offerings? Hint: a change in quality of speaker is FARRRR easier than- say- making Siri a lot better than Alexa for that purpose.
With this query, the best you are going to get is a situation where maybe someone has access to the same movie from both sources by some odd circumstance where they've paid and/or been given access to the same movie from 2 platforms, and opted to keep 2 copies of the same movie anyway. Then, you get a
subjective comparison of 1 or 2 videos, from a generally-biased judge who probably worships at the alter of Apple in all things. They probably have NOT compared the same video at the same time and maybe not even on the same equipment, as we're generally not a bunch of scientific-minded critics, ready to watch a movie twice in one sitting and see if we can see & hear what is probably only fine detail variations of quality. Etc.
Besides when Apple had more market share than all competitors, we proudly touted Apple as #1 in market share. When they lost their hold on #1, we move the goal posts to "but who has the most profitable...". Again, we generally want Apple to win at all things. It's hard to get objective answers in such a biased group.
Bottom line: this is very much an eye-of-the-beholder quest. The best strategy to get a good answer for you would be to do a bunch of head-to-head testing yourself, on your own equipment, in your own living room, at the same point in time. If you believe you are a overly Apple-centric yourself, enlist someone to help you do a blind head-to-head test by not telling you which source is running on which television. Anything else allows way too many unstated variables to creep into the evaluations from a very biased crowd in general.
For example, if one:
- watches a favorite movie on a friend's television and hears it through that friend's speakers and then
- watches it again on another friend's television and hears it through different speakers and then
- watches it yet again at home on their own television and hears their own speakers,
...a clear winner may be crowned even if ALL 3 setups were playing the exact same movie from the exact same source. Friend #2 might not have Dolby Digital turned on and your ears might notice that ProLogic (faux surround) didn't sound quite as good as #1 or #3 (or maybe your ears thought it sounded better). #1 might not have their picture settings optimized on their TV, so the video on their set might not look as good as #2 and #3. You might have inferior speakers and/or an inferior TV, so the video might sound or look worse on your TV vs #1 & #2. Friend #2 might have served some bad burritos that upset your stomach during the movie and you just remember it as a worse experience. Friend #1 might have been a supermodel who really, REALLY dug you that evening and you remember the whole experience as being world-shaking, best-ever, without even actually watching much of the movie. Maybe friend #1's cats were irritating the h*ll out of you throughout the playback and you subconsciously hold that against the evaluation? Etc.
Answering a question like yours might involve recalling watching the movie in such scenarios and recalling that #1 was definitely superior to #2 and #3 or vice versa... with no mention of different TVs, different sound systems, different playback hardware, unoptimized settings, allergies acting up, the influence of cats/dogs/iguanas/kangaroos/giraffes/spiders/pigs/reptiles/tribbles/goats/aliens, supermodels, noisy neighbors, bad burritos, (live) drama (not in the movie), inferior broadband, AC/heat settings, phone calls/notification prompts, lighting differences, forgot the glasses/contact lenses that day, inferior cables, etc.
