I guess it is quality vs quantity.
Tsukuyomi is easily a strong genjutsu that ends pretty much any 1 on 1 fight...but compared to the genjutsu of KA it doesn't stand ground....Tsukuyomi destroys someone's mind where KA allows you to control them...controlling a mind is more useful then destroying as it leads to more stealthy antics, and an unlikelyhood of getting detected.
The trade off is that KA is a once in 10 years Jutsu...Tsukuyomi is more readily available!
So the need for a situation could give either one a better advantage.
So either Quality (mind control KA) or Quantity (mind breaking Tsukuyomi)