Is it better to sacrafice sleep or exercise in order to feel rested?

Depends. You will sleep better if you exercise regularly. However, you will not have your best outing if you are sleep deprived. Goal would be averaging 8 hours of sleep per night (some adults need more). Then "schedule" in your exercise time based on all the other things that need to be done in a day. Try to put sleep and exercise at or near the top of the list.
Sleep. The usual amount of sleep needed is 6 to 8 hours per most studies for most people.