Which is better for a worshiper unable to stand for the entire prayer: leaning against a wall or sitting?

Standing during the obligatory prayer (fard) is obligatory by consensus, and it is not permissible to sit unless one finds standing difficult. If one cannot stand except by leaning on a wall or similar support, then standing is still obligatory.

As for the supererogatory prayer (nafilah), it is permissible to sit even if one is able to stand, and in this case, one receives half the reward of the one who stands. If one is able to stand by leaning, that is preferable. Leaning on a stick during supererogatory prayers is permissible by agreement of the scholars.