Which is better and more rewarding in the sight of Allah: sitting to recite the Holy Qur’an as a daily habit, or going to a mourning tent to recite the Qur’an after performing the burial and offering condolences at the grave?

Offering condolences to a Muslim is commendable at the grave and should not be repeated. Gathering for condolences is considered a form of wailing (niyāḥah), and gathering to recite for the deceased is an innovation (bidʿah). As for your gathering for recitation, if it is for study and memorization, then it is a good deed. However, if the recitation is done collectively and in a single voice, then it is a reprehensible innovation that should be avoided.