I think it depends on the feel of the song, And how many people are on the track or in your group. Ex You and your 2 boys are making a track You spit 8bars and end that eight with something your other boy can work off to finish the other eight...... If that made sense. You could go with 12 bars verses aswell!
all depends on the type of beat tempo & artist you iamgine on it really, but 16 is usually standard with 8 bar hooks. Never stick to same all the time though switch it up once you understand it all.
I use 12 bar verses often, 8 bars seems way to short unless the beat is in the 60's for tempo. Anything above 80 bpm I almost always use 16 bar verses.
When arranging a track, I think it's best to do whatever has the most impact on the intended listeners. Listeners and followers keep the music industry alive. Do everything you can to entertain them.