To choose the best caption for the photo, we need to consider the context of the image. If the photo depicts people enjoying outdoor activities, a picnic, or being in nature, then "Vamos al campo los domingos" would be the most suitable choice. If it shows a group at church, then "Vamos a la iglesia los domingos" would be appropriate.
Without the image for context, if I need to recommend based purely on common Sunday activities, "Vamos a la iglesia los domingos" is often a strong choice. However, "Vamos al campo los domingos" could be equally fitting for more recreational activities. Ultimately, you'd want to match your choice to what the photo represents.