Jacknyoc - If you really will be a light user (two or less journeys per day in the central area) then "pay as you go" will be cheaper than loading a weekly travelcard. If you are likely to make three or more journeys for five days or more, the week travelcard will save you money. Because of the lower daily cap for journeys in central zone, you won't be out of pocket by more than a few pounds, even if you pick the "wrong" option.