I think my favoured amount of sleep would be around 8-9 hours, but I usually only get 6-7 hours and quite often less. If I get less than 5 hours sleep I really feel it the next day, especially in the morning.
Everything I read about sleep points to it being a critical aspect of health and fitness. Right up there with nutrition and exercise. I also read that sleep quality has a tendency to degrade with age.
Key points for sleep quality seem to be sticking to a fixed sleep routine i.e. going to bed and waking up at the same time each day. Also relaxing and unwinding an hour or two before bedtime and avoiding exposure to bright lighting (e.g. mobile phones, tablets etc)