Remember, never ever lie to yourself or ignore your feelings.
So on my rest days i just bounce around the house having fun.
Since I exercise 5 times per week, I usually have a rest day after two or three days with exercise.
Unless of course I am on a 20 week preparation for a 42km marathon and am following a programme that includes the other days.
Even then, there would be rest days allotted to the program.
But following my morning journey in Fabulous, I've been doing my small workout every single morning to make it a habit. I keep it simple and small to make sure that I can always fit it in, and found this very helpful.
So I personally think that it's best to do some exercise every single day, but maybe leave some time between bigger workouts.
Hope that helps!