I would like to know which poems of Baroque poets Herbert and Gryphius are the easiest to compare in terms of the imagery they use?
This is an interesting topic you suggest. Baroque (1600-1750) poets George Herbert (1593-1633, England) and Andreas Gryphius (1616-1664, Germany) wrote on such vastly different subjects that their styles in using imagery--as called for by their subject matter--were equally different. Gryphius (latinized from the original Greif), born and reared in the midst of the Thirty Years' War and eventually driven from his home by it, writes of destruction and "the maddening music of war, / The sword fat with blood" and of the Earth that "is empty show" for "What blooms so fair at daybreak, by noon is trampled low" and of birth and death while "breathing the smoke of war, ...." These quotes are from Gryphius's poems "Tears of the Fatherland," "The Vanity of This World," and "Epitaph for Mariana Gryphius," respectively.
In contrast, Herbert writes of unrequited love, "Therefore my soul lay out of sight, / Untuned, unstrung: / ... / Like a nipped blossom"; spiritual restoration, "to be Thine doth me restore, / So that again I now am mine"; and temptations to ungodliness, "When suddenly I heard one say, / -Do as thou usest, disobey." These themes derive from "Denial," "Clasping of Hands," and "Artillery," respectively. As a result of the differences, a comparison of their imagery may yield complex results. I'd suggest you start with these six poems since each has imagery you can examine and analyse while you build your theory of the poets’ approaches. Bear in mind that subject matter will at least in part dictate poetic imagery style.