Here's my ranking:
1. Blu-ray (Japan): I agree with all the criticisms you have with this cover, 
Marce82, and I think the Zavvi Steelbook one is better, but I personally prefer this one mainly because it feels more mysterious in the sense that it doesn't reveal so much about the movie as the steelbook.
2. Zavvi Steelbook (UK): I love this one too and I agree with everyone else that it's a great cover.
3. Blu-ray/DVD: I don't mind the poses, given that as 
Marce82 pointed out, the movie also has adventure, but I'm not a fan of the expressions here or on most of the other covers. However, I think this is not a bad cover and I like the background and how it's framed by the trees/bushes.
Marce82 wrote:I appreciate the inclusion of the tower... that tower is almost a character in the film.
I completely agree. I also like that it's included.
4. 3D Blu-ray (Korea): I think this is one of the covers that wants us to believe this movie has some twist and it's not just a direct adaptation of the fairy tale, but it's actually quite beautiful.
farerb wrote:I really like that cover, D82. Somehow I feel like it represents the film better than any other cover.
Well, though that exact scene doesn't happen like that in the final film, it shows some of the most iconic elements from the fairy tale like the tower or Rapunzel's long hair and feels quite magical thanks to the beautiful setting, so I think you may be right after all.
Disney Duster wrote:I really like that cover too! But Rapunzel never looked like that in the movie to me.
Yeah, she has that same malicious smile she has on many of the covers.
5. 3D Blu-ray (France): To me both Rapunzel and Flynn look like wanted thieves here, even though their faces are the same as in the Blu-ray/DVD. I don't like nor hate the concept, but I find a bit stylish that it's almost monochromatic with the title being golden like the hair.
6. 4K Best Buy Steelbook Exclusive: It's kind of cool that the image continues on the back, but I agree with 
Marce82 that the front doesn't really work on its own and I prefer when the do. Plus, I can't believe they used this art that supposedly includes a subliminal message.
7. 4K UHD (Japan): I would've ranked it higher if not for the uninspiring background.
8. 3D Blu-ray: I never liked this one because I don't like the mix of night and day elements in the background.
9. 4K UHD
10. Heroes Cover (France) 
11. Heroes Cover (UK) 
12. Villains Cover (UK) 
13. Villains Cover (France) 
14. Disney Princess Cover (Australia): I like the pose, but it looks like a weird combination of 2D and 3D animation to me. I think they should've adapted the design to 2D instead of tracing it from a still from the movie and just paint it like a 2D image, which it's what it seems they did. I think they used this still and just rotated it a bit:
 
 