A while ago, I blogged about a plan by Steven Spielberg and Peter Jackson to produce a Tintin trilogy.
It looks like they've chosen the stories for the first film: "The Secret of the Unicorn" and its sequel "Red Rackham’s Treasure" (both will be covered in one movie). Those were two of my favorites, and I think that's a good place to start, even if they aren't the first books in the series.
The first few Tintin books — "Tintin in the Land of the Soviets," "Tintin in the Congo" and "Tintin in America" — all have elements that would probably distract someone who was new to the series. Plus I'm not sure if "Soviets" was ever published in English (I have a French copy), so that limits the fan base. "Red Rackham" also introduces Professor Calculus, a cherished character.
They're going to use performance-capture technology to make the films (like with "Beowulf" or "Polar Express"), which is usually pretty creepy. But it's probably a good call here since it's hard to find an actor with Tintin hair.