As both an educator and singer, I have always been fascinated and stimulated by the process of analyzing options for the key that a given tune might be played and sung. Of course, the ultimate choice is up to the singer performing the song.
As a vocal instructor, I notice that students will sometimes question, or even resist, changing the key of cover tunes that we work on in lesson.
I’ve found that at the outset, it’s a worthwhile exercise to examine a tune’s melodic range, as well as phrasing, potential breathing challenges and then the movement of the melody ascending and descending.
Sometimes changing the key is the answer if we can’t reach a note, but sometimes we can alter the melody slightly, and keep the key the same- without changing the overall “feel and sound” of the melody. Additionally, we may consider a key change just to create a unique overall sound of a song- regardless of any technical vocal challenges.
Remember that the singer in the original recording of a song has their own unique vocal range. And then the key of the song was chosen according to that range and voice. Unless you have the exact same vocal range and voice, you must choose the key that is right for you.