the best editions of Mark Twain's works are those that come out
of Berkeley's Mark Twain Project. Therefore, the best choice for
Roughing It would be:
Twain. Roughing It. Edited by Harriet Elinor Smith, Edgar
Marquess Branch, Lin Salamo, and Robert Pack Browning. U of California
Press (December 2002). ISBN-10: 0520238923. ISBN-13: 978-0520238923.
The Innocents Abroad is not yet available from the Mark