Voice Leading Priorities

In an ideal scenario, at least in rather traditional 4-part writing, every voice of a composition should have its own plausible melody or at least proper voice leading while still serving its function in the vertical structure (e.g. providing the necessary chord tone to fill up the chord). This is not only to please any musicians who play your music (and of course would love to have plausible melodic parts in their voice) but it will also increase the attractivity of your music to the ear, no matter whether all these lines are consciously perceivable. While music has developed quite a bit since traditional 4-part harmony, however the ideal of giving each part a nice melodic structure still is valid.

Naturally, achieving this state is quite tricky and you regularly end up with one or two middle voices that tend to become melodically rather unattractive. Unless you spend lots of time figuring this out or have a tremendous control over your writing you will most likely need to prioritize which voices should be favoured in voice leading and which ones are ok to "suffer". Note that every change you make in this regard has consequences on a larger scale so fixing one "weird step" in one part will most likely make it necessary to adjust another line which then might become worse etc.

Our ear puts most focus on the outside lines, meaning the highest and the lowest in the structure. Usually the lowest is the bass line but if you for example have the bass notes played by the Double Basses and a "Horn Chorale" on top of that, then due to the different textures our ear will also be able to distinct the lowest horn part so it would be benefitial to put melodic focus on that as well.

As a consequence, the best strategy usually is to work from the outsides to the insides, starting with highest and lowest voice and then gradually filling up the voices with as good as possible voice leading until you end in the "middle" most likely with a rather unattractive voice that needs to fill up missing chord tones etc. With this strategy you will be able to have nicer voiceleading on more perceivable lines and less attractive voice leadings on lines that probably get buried anyway.

Just as a clarificiation: voice leading doesn't necessarily mean that it needs to be a super active line, however also lines that move in whole notes can have an attractive musical contour.