Best for mostPenguin Classics · 2003
Moby-Dick rewards a little help — the whaling chapters and the Biblical and Shakespearean echoes go by fast. Penguin's edition gives you exactly enough: Andrew Delbanco's fine introduction, Tom Quirk's clear notes, and a clean, affordable text. Not so much apparatus that it gets in the way. This is where I'd start.
Best for studentsNorton Critical (3rd ed.) · 2017
The student's Moby-Dick. The reliable text, plus illustrations, whaling background, and forty-odd reviews and essays spanning three centuries. If you're studying the novel, or want the whole conversation around it, this is the one. More than a casual reader needs, and priced accordingly.
Most annotatedLongman (Bryant & Springer) · 2006
The most annotated Moby-Dick in print. Bryant and Springer pack the margins with explanation, and — unusually — flag the passages Melville and his British publisher revised, so you watch the book change under your eyes. Fascinating if you love the textual history; expensive, and more than most first readers want.
Most beautifulPenguin Deluxe · 2009
The Penguin Deluxe edition — Tony Millionaire's cover, deckle edges, Nathaniel Philbrick's introduction. The same readable text as the standard Penguin, dressed up. The one to buy if you want Moby-Dick as an object on the shelf.
Herman MelvilleMoby-Dicktr. Free (public domain)
FreeFree (public domain) · 1851
Moby-Dick is out of copyright, so the full text is free — Project Gutenberg, Standard Ebooks, and others. No notes to catch the allusions, which this book really does benefit from, but if you just want to start, it costs nothing.