Much of how you choose a text depends on what sort of coverage interests you. There are many anthologies covering all of English poetry. Some are more traditional, focusing on "the best that has been thought and said" and some make more efforts towards race, class, and gender diversity (though those often are heavily weighted towards more recent poetry). There are three flavors of anthology you can choose from:
- Just poems (least expensive, but you need to supply extended study notes)
- Poems with explanatory and biographical notes (the Norton is the standard for universities)
- Textbooks with full teacher aids including explanatory materials, instructor manuals, sample tests and assignments (X. J. Kennedy, Introduction to Poetry is a good textbook)
When I want just poems, I simply select the poems I want from free copies on the internet or .make .pdf files of public domain works in libraries and put them on my course website (you can email a file to students if you don't have a website).
If you are looking for a textbook, ask the publisher's representatives assigned to your school from the major textbook publishers to send you examination copies so that you can select something appropriate to your curricular needs.