You really need to consider which translation of
Les Misérables to opt for (assuming you plan to read it in English).
The Hapgood translation is the one that was used for Project Guthenberg, and which therefore is probably the one you'll find in most public domain versions (including the one here in the MobileRead library).
But there are a couple of more recent translations that you might find easier to read. These are by Norman Denny and Julie Rose respectively. Since both of these translations are recent, they will still be in copyright, so you will have to pay the going rate for the e-books.
The Signet Classic is based on the original American translation (by Charles Wilbur), but has been modernised.
(
Source for all the above.)
In short, your best bet would be to download samples of each, and to decide which translation you prefer, and which version has the fewest errors and the best formatting.
One other thing to keep in mind is whether you prefer to read an American or a British translation. In theory, it shouldn't matter - they are both equally valid. But many people think otherwise.
Please let us know which one you finally decide on.
Mike