Unquestionably the first. A piece of art should stand by itself as a whole. Anything detracting for this dilutes its impact. A still image within the context of a 90-minute movie is so incredibly diluted compared with an artistic print which forces your focus on it. (If that all makes any sense.)
Or, since I think in terms of photography, take two photographs: one cropped to produce an iconic image, and the second uncropped with a lot of extraneous (and perhaps even distracting) detail. Now the second photograph contains the first, but the impact of it is diluted due to all the impertinant crap surrounding it. It’s not better. Not at all.
It’s possible for a work to be greater than the sum of its parts. It’s also possible for it to be less. If the movie’s only redeeming feature were that one frame, then I would say that it is the inferior piece of art.
If I judge the movie as a whole, it’s a failure, only partly redeemed by its one, good moment.
It’s just like asking. . .what would you rather eat, a spoiled turkey, or a spoiled turkey stuffed with candy? What does it matter when either one is going to make me sick?
Part of artistry is knowing what to leave out. Would you rather have the Mona Lisa, or the Mona Lisa with a mustache? A single pearl is nicer than a similar pearl dipped in pigeon poop.