I've always greatly preferred excluding "The"--even if Twain himself didn't
care much--because its absence suggests that Huck's adventures are or might
be open ended. The book closes with himnds with him on the run . . . which
leaves the possibility of more adventures to come.
As for Kevin's comment, I've always been happy with THE HAMLET as a title.
It also fits well with its sequels--THE TOWN and THE MANSION. It's maybe
Faulkner's funniest novel, and features V.K. Ratliff, one of my favorite
characters, and one who shows Faulkner's great debt to Twain. . . . But I
reckon it could be Kevin had that play about the Great Dane in mind, rather
than Billy Faulkner.