Am interested in feedback from anyone who has taken either of the tours offered by the Vatican itself (the Vatican Museum including Sistine Chapel or the Vatican Museums and St Peters) re: suitability of tour length, guides knowledge level / language skills. Did you feel the additional cost was money well spent or would a good guide book suffice(open to recommendations here - a friend has recommended 'Mona Winks')? We are first time visitors to Rome, traveling with 13 / 15 year old, interested in all things historical but not very knowledgeable about art.