The denominations built around a single supreme deity give ishta-devata its sharpest edge. Vaishnavism holds Vishnu, most often approached through an avatar such as Krishna or Rama, to be Para Brahman itself, not a favored member of a pantheon but the ultimate reality of which every other deity is a lesser expression. Shaivism makes the identical claim for Shiva, and Shaktism for the Goddess in one of her many forms, from fierce Kali to benign Parvati. Each of these traditions can therefore speak, in its own literature, in the exclusive language of monotheism, God's supremacy stated without qualification, while still operating inside a shared Hindu framework that recognizes the others' devotion as reaching the same reality by a different face.
Smartism turns the same doctrine outward rather than inward. Rather than asserting that one deity is supreme, it holds, following Advaita Vedanta, that Brahman is beyond all form and that Vishnu, Shiva, Devi, Surya and Ganesha are five equally valid doorways to it, so a Smarta household's ishta-devata is a matter of personal disposition, not doctrinal necessity, formalized in the panchayatana puja that sets images of all five side by side. Sri Vaishnavism narrows the Vaishnava case further still, taking Vishnu specifically as Narayana, never separate from his consort Sri, the source of the tradition's own name. Across all these readings, the underlying grammar is the same: a real, particular devotion to one chosen form, held inside a wider claim about what stands behind every form.