If you buy the version with Tintin standing on the rocks on the front cover, this is the 1943 version, much closer to the 1938 black and white original, except for 4 changes.
If you are buying the version with Tintin in a boat on the front cover, you are buying the 1966 version rewritten by the translators Leslie Lonsdale-Cooper and Michael Turner and redrawn, in conjunction with Herge.
This 1966 version contains some 300 changes including replacing all of the cars, boats, trains and uniforms with more up to date or 'accurate' drawings, not by Herge himself, the 'violence' has been toned down and there are some minor changes to the story.
The 1966 book is less of a Herge work of art and more of a exercise in political correctness and marketing for the English audience and as a result loses much of its original charm.
They are two entirely different books, both good in their own right, personally I own both versions in English and French, but if i had to choose just one, i would go for the 1943 version - Remember, the one with the front cover showing Tintin on the rocks, not in the boat.