Personally, when it comes to which ending that I believe to be the best of them, I've found myself in a tie between Rainbow Dash and Fluttershy's ending. I enjoyed Rainbow Dash's because of how fun to watch it was, and it made sense that exercise could reduce how stressed you feel. I also enjoyed Fluttershy's because her ending was the most logical, in that a good nap and taking time to relax is always a great way of reducing how stressed you feel. Now that I think about it, I think Fluttershy's is the one that I consider to be my headcanon ending.

As for Pinkie's ending...well, I honestly consider that one to be the more annoying of the three. I couldn't get how Pinkie constantly popping out of nowhere and bothering Twilight would help her relax, because I think that would stress her out more than relax her.

But, all that is my opinion.

Which ending do you guys like the most?

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Fluttershy's ending was hilarious with Twilight cuddling with skunks without even realizing it. When she wakes up and scares the skunks with her scream, they spray her, she'll need a long tomato juice bath.

I like Rainbow's

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The one with Rainbow Dash.

The one with Fluttershy, cause with the animals it was adorable.

Rainbow Dash

I personally think Fluttershy's ending would be the canon ending, since she definitively helped Twilight to relax (personally, exercising would get me more pumped up to do more, not relaxed and destressed, but that's just me).

7644305 First one, but only because I like seeing Rainbow Dash in her skintight leggings.

Fluttershy's ending!