And he said to them, “Therefore every scribe who has been trained for the kingdom of heaven is like the master of a household who brings out of his treasure what is new and what is old.” Matt 13: 52 NRSVCE
That is what meditating on the Mysteries of the Rosary is like. One trip through the Rosary yields insights. The next time through, there are fresh ones. Over time they accumulate in the memory and together yield yet newer treasures.
I think that is the basis of “favorite Mysteries” of the Rosary. They are the ones where we have large accumulations of treasure, and Jesus did say that where our treasure was our heart would be too!