Is it better for this world and the Hereafter to continue memorizing a small portion of the Qur'an during free time, or to return to frequently invoking blessings upon the Prophet (peace be upon him), especially since the time allocated for memorization does not allow for combining both?

The Holy Quran is the best type of dhikr (remembrance of Allah), and engaging in memorizing it during free time is better than other forms of dhikr. It is preferable to memorize the Quran by heart, as it is stated in the Hadith: "It will be said to the companion of the Quran: 'Recite and ascend, and recite as you used to recite in the worldly life, for your status will be at the last verse you recite.'" This applies specifically to one who memorizes it by heart, not to one who reads from the Mushaf (copy of the Quran).

However, if invoking blessings upon the Prophet (peace be upon him) is more beneficial for the heart—for example, due to an inability to memorize and ponder the Quran—then invoking blessings upon the Prophet is better for that individual. This is because a less meritorious act may be better for a specific person due to particular reasons, such as benefiting more from it, or being unable to perform the more meritorious act.

Based on this, reciting the Quran is better than the general category of dhikr, and the general category of dhikr is better than the general category of du'a (supplication). However, a less meritorious act may be accompanied by something that makes it better than others, either because it is prescribed for all people at specific times and places, or due to the varying circumstances of people, such as someone unable to memorize the Quran. In this case, a person may find more presence of heart and strength of faith in dhikr than they find in reading the Quran.