Best for mostFolger Shakespeare Library · 1992
As with the rest of Shakespeare, the Folger is the easiest way in — notes facing the text, so you read Macbeth without constantly dropping to the bottom of the page. It's the shortest of the tragedies and moves fast; the Folger keeps you moving with it. Cheap and clear. This is where I'd start.
Most scholarlyArden (3rd series) · 2015
The Arden Third Series Macbeth, edited by Sandra Clark and Pamela Mason — the full scholarly treatment, with a long introduction and dense footnotes on the text, the witches, and the play's tangled history. The reference edition for serious study; more than you need for a first read.
Best one-volume scholarlyOxford Shakespeare · 1990
Nicholas Brooke's Oxford edition is the strong one-volume scholarly Macbeth, and it's especially good on a real puzzle: the play survives only in the 1623 Folio, and parts of the witch scenes were likely added later by Thomas Middleton. Brooke walks you through all of it. Excellent value for the depth.
For beginnersNo Fear Shakespeare · 2003
No Fear sets the original beside a modern-English paraphrase. You lose the poetry — and Macbeth is some of Shakespeare's densest, most compressed verse — so treat the modern side as a helper, not the real thing. But if the language has defeated you before, it can get you through to the end.
William ShakespeareMacbethtr. Free (public domain)
FreeFree (public domain) · 1623
Macbeth is public domain, so the full text is free — Folger Digital Texts, MIT, Project Gutenberg. No glosses for the harder lines, of which this play has many, but it's the whole thing at no cost, good for a re-read or to sample before buying.