Apparently, per Wikipedia, the 1818 edition is the original:
"On 31 October 1831, the first "popular" edition in one volume appeared, published by Henry Colburn & Richard Bentley.[26] This edition was heavily revised by Mary Shelley, partially because of pressure to make the story more conservative, and included a new, longer preface by her, presenting a somewhat embellished version of the genesis of the story. This edition tends to be the one most widely read now, although editions containing the original 1818 text are still published.[27] Many scholars prefer the 1818 text, arguing that it preserves the spirit of Shelley's original publication (see Anne K. Mellor's "Choosing a Text of Frankenstein to Teach" in the W. W. Norton Critical edition)."
http://www.gutenberg.org/ebooks/84
LibriVox Free Audio Recordings:
https://librivox.org/frankenstein-or-...
https://librivox.org/frankenstein-edi... (1831 edition)
https://librivox.org/frankenstein-dra...
https://librivox.org/frankenstein-by-...
https://librivox.org/frankenstein-or-... (1818 edition)
Apparently, per Wikipedia, the 1818 edition is the original:
"On 31 October 1831, the first "popular" edition in one volume appeared, published by Henry Colburn & Richard Bentley.[26] This edition was heavily revised by Mary Shelley, partially because of pressure to make the story more conservative, and included a new, longer preface by her, presenting a somewhat embellished version of the genesis of the story. This edition tends to be the one most widely read now, although editions containing the original 1818 text are still published.[27] Many scholars prefer the 1818 text, arguing that it preserves the spirit of Shelley's original publication (see Anne K. Mellor's "Choosing a Text of Frankenstein to Teach" in the W. W. Norton Critical edition)."