There is no difference between the worshippers of Ishwara as the sakara (having a form) and nirakara (formless) because both are capable of attaining Ishvara in the end. Devotion to the nirakara is somewhat difficult to practice, because the immutable supreme cannot be known or grasped by the senses and the mind.
According to the Bhagavad Gita there are four types of devotees
– the sufferer, the seeker of knowledge, the seeker of worldly objects and the
man of wisdom (VII.16). Out of the four, the man of wisdom is supposed to be the
best, since the devotee of this type constantly identifies himself with Ishwara
and possesses exclusive devotion. Apart from that, he does not have any selfish
interest or desire. Ishvara is extremely dear to him and he, the man of wisdom,
is extremely dear to Him (Bhagavad Gita VII. 7) all other types of bhaktas are
also noble, but the man of wisdom realizes that all is God. Such a great soul
is rare.
In the Bhagavad Gita, bhakti has been divided into three
kinds – satvika, rajasika and tamasika. In sattvika bhakti, men of sattva
nature (intelligence or purity) worship the gods; in rajrasika, the men of
rajasika nature ((energy or passion) worship yakshas and rakshasas and in
tamasika bhakti, person possessed of tamas (mass or dullness) worship pitrs and
ghosts.
As far as bhakti is concerned, the duality is maintained throughout between the worshiper and the worshiped. This state is maintained even after the liberation of the individual soul.