It really depends on the original I think.

Eg. As I was talking to @astro_penguin about it yesterday.

Iron maidens wasted years original, quite fast quite heavy, great track. https://youtu.be/Ij99dud8-0A?si=7MwkgfJOGZzBHuii

But the carved in trees cover slowed it right down and bought an entirely different perspective to the track https://youtu.be/rTZVHMP_vpY?si=a7Jw2Teg7jC14s_S

But does it work the other way? Yes, yes I think it does.

Better Midler - wind beneath my wings, beautiful, soft, slow, ballad. https://youtu.be/0iAzMRKFX3c?si=-Y8xWkdm47UxQ52a

Sonata Arctica cover more power metal ballad, sped up, different perspective again. Great version. https://youtu.be/kzapwP5Z9kA?si=ikgHcW0UscaoMqit

I think the choice for me isn't as black and white as fast or slow, it's more based on the original and the new perspective that the cover brings.