Wake up naturally if you can. On the weekends is when most people decide not to do this. You wake up at whatever time, but you know it's Saturday, so you go back to sleep. Then you wake up tired for the rest of the day. In psychology I learned why this works the way it does, your energy follows a circadian rhythm that naturally waxes and wanes throughout the day. If you wake up naturally, you come awake as your circadian rhythm is on it's up cycle, but if decide to sleep more, you most often awake when it's on a down cycle and your energy is going down.
