My husband and I are planning an 8-day trip to Mexico City the last week of September and we are really looking forward to it. We would really like to squeeze in Queretaro, San Miguel Allende or Guanjuato as a side trip and only have one full day to dedicate to one of these towns. I know each town has so much to offer but any recommendations on which to choose if only one? Your input is greatly appreciated! Thank you.