Best for mostFolger Shakespeare Library · 1992
For almost everyone, the Folger is the right Romeo and Juliet. Notes face the text, so you read without dropping to the bottom of the page — and this play's wordplay and bawdy puns really do need glossing. Cheap, clear, and the classroom standard. This is where I'd start.
Most scholarlyArden (3rd series) · 2012
The Arden Third Series, edited by René Weis, is the scholar's edition — a long introduction and footnotes that cover the text's history (the play survives in competing early quartos) and every crux. Indispensable for study; heavier than a first read needs.
Best one-volume scholarlyOxford Shakespeare · 2000
Jill Levenson's Oxford edition is the strong middle — serious scholarship in one affordable volume, with an excellent introduction on the play's sources and stage history. The step up from Folger without going all the way to Arden.
For beginnersNo Fear Shakespeare · 2003
No Fear puts the original beside a plain modern paraphrase. Purists wince, and you lose the poetry — but if Shakespeare's language has stopped you before, it can get you through, and you can lean on it less as you go. Training wheels, honestly labeled.
William ShakespeareRomeo and Juliettr. Free (public domain)
FreeFree (public domain) · 1597
Romeo and Juliet is public domain, so the full text is free — Folger Digital Texts, MIT, Project Gutenberg. No glosses for the puns and archaic words, but it's right there at no cost for sampling or re-reading.