To summarize Coleridge's own words (excerpt added above), a good poet inspires deep emotion through energizing the commonplace by instilling it with fresh perspective and newness: "in the balance or reconciliation of opposite or discordant qualities." A good poet harnesses their whole powers of "worth and dignity" to infuse words with a "tone" and "spirit" that epitomize "imagination": the cognitive power that synthesizes observation with original perception to create new conception; creative power. A good poet is one that recognizes the proper order of subordination (i.e., importance): art is subordinated to nature (no false artifice called "art" is greater than nature); the manner of expression is subordinated to the matter expressed (no irrelevant subject expressed as poetry can be good poetry, which must have noble subject matter); and the poet is subordinated to poetry (the creator is incidental to a moment in time while the poetry is for all time).
The word "contemporaries" is a bit awkward to work with. By one definition, Coleridge's (1772-1834) contemporaries span from Pope (1688-1744) to Keats (1795-1821). By another definition, Coleridge's contemporaries are only those of his own generation, which might include Blake (1757-1827), Wordsworth (1770-1850), and Lord Byron (1782-1824).
Choosing "who among his contemporaries fits the description best" is also difficult to work with and depends upon opinion, perhaps a professor's opinion or a student's guided opinion. Without stating an opinion, let's explore some possibilities on which an opinion might be founded. Taking the larger view of "contemporaries," let's point out that Pope might not fit Coleridge's definition since Pope's rigid stylistics helped inspire the reaction that became Romanticism. Blake might not fit because Coleridge and Wordsworth thought him a bit mad. Going down to Keats, he might not fit because his style was thought a bit untempered, a bit loose, with too much Classicalism to it (this problem of style is seen in his meter, which breaks down at intervals, and is most likely due to the effects of his tuberculosis). Wordsworth is the most likely fit--aside from himself, of course--since they felt in enough simpatico to be co-contributors to Lyrical Ballads. It must be noted that Coleridge made clear in Biographia Literaria that Wordsworth did not speak for him in the Preface and that they had several points of disagreement. Others who might fit are Byron and Shelley (1792-1822).