"Lord Siva's symptoms of austerity are not exactly those of a Vaisnava. Lord Siva is certainly the number one Vaisnava, but he exhibits a feature for a particular class of men who cannot follow the Vaisnava principles. The Saivites, the devotees of Lord Siva, generally dress like Lord Siva, and sometimes they indulge in smoking and taking intoxicants. Such practices are never accepted by the followers of Vaisnava rituals."

Srimad-Bhagavatam 4:6:36 Purport

Prof. Hopkins: You would say impersonalist.
Prabhupada: Oh yes. They say Sivaham, "I am Siva." They are impersonalist. If you are Siva then why you worshiping Siva? That is impersonalist.
Prof. Hopkins: So any position which would deny the difference between the devotee and God, you would see...
Prabhupada: He is impersonalist.
Prof. Hopkins: Is impersonalist.
Prabhupada: The impersonalist theory is that I am now devotee. As soon as I become perfect I become one."
Prof. Hopkins: Oh.
Prabhupada: That is their theory. Then there is no more difference. In the preliminary stage, when I am not perfect, I am worshiping some imaginary form of God. But when I become perfect there is no need of worshiping, I become one with God. This is impersonal. Now, actually, the Supreme has no form so they recommend whichever form you like to worship you can select out of these five. But their destination is the same. So somebody likes "I worship Siva," somebody says "I worship Ganesa," somebody says, "I worship Durga," and Surya, or somebody says, "I worship Visnu." So this Vaisnava is impersonalist. You'll find amongst smarta brahmanas there are also some of them Vaisnavas, but they are impersonalists.
Prof. Hopkins: So you would... You would say that those, those smartas say, and I know smarta brahmanas who are worshipers of Visnu. You would say they still are impersonalists in some ultimate sense because at some point they would deny...
Prabhupada: No, it is very difficult to pick them out. Most of the so-called Vaisnavas, they are impersonalists.
Prof. Hopkins: Some, I suspect, are more Vaisnavas than they are smartas.
Prabhupada: So, satatam kirtayanto mam? Brahmananda:

satatam kirtayanto mam
yatantas ca drdha-vratah
namasyantas ca mam bhaktya
nitya-yukta upasate

"Always chanting My glories, endeavoring with great determination, bowing down before Me, these great souls perpetually worship Me with devotion."
Prabhupada: Perpetually. It is not that I am worshiping now and when I am perfect I become one. That is impersonal.
Prof. Hopkins: But someone who sees devotion as the not just a stage...
Prabhupada: They say everything one; no devotee, no devotion, and no person. Everything becomes one.
Prof. Hopkins: So that would then be the deciding test, as it were, of whether one were a serious devotee or not.
Prabhupada: Devotee means serious devotee.
Prof. Hopkins: Not only that one is devoted now, but that one sees the goal as perpetual devotion.
Prabhupada: Yes. Nitya-yukta.
Prof. Hopkins: And which never is there...
Prabhupada: The word is used, nitya-yukta. Nitya-yukta means perpetually. If a devotee is to merge into the existence of the Lord then why this word is used, nitya-yukta. Upasana. Not only nitya-yukta, upasana. Upasana means "you worship Me." As soon as the word is "he worships" that means the worshipable and the mode of worship and the worshiper must be there. That is indicated, nitya-yukta, perpetual. But the Mayavadis or these impersonalists, they think that it is temporary. I am devotee temporarily. As soon as I become perfect I become one.
Prof. Hopkins: So that you would see then, in terms of, in terms of some kind of theological structure, you would see that Purusottama as always...
Prabhupada: Uttama, uttama means the best.

Srila Prabhupada Room Conversation, 7-13-75, Philadelphia

Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.