I like Martin Freeman and think he is best realistic candidate but I don't think he is perfect if you think of the book Bilbo who is a Tookish freespirit trapped in a very bourgeouis conventional exterior. Freeman does the ordinary bloke caught in odd circumstances well and he was good as Arthur Dent - a more modern arthur Dent than the posh "silly ***" type played by Simon Jones.
However Richard Armitage... I might even go and see this misbegotten movie if it has Hugo Weaving and Richard Armitage.
And I would love Bill Nighy to play Galion... I know I have said this before but noone does dissipation like him..save perhaps Richard E Grant...