Storytelling - goes to Dreamfall. Gameplay - I'll give the nod to TLJ.
I don't see the opposition any more. Probably because I don't want to. Game designers are searching for that ultimate way to merge gameplay and storytelling. Players are in argument whether that is actually possible, good gameplay AND a good story, neither to the detriment of each other. Yet for many, artful adventure game puzzles are a solution to the problem already, and a good one at that. The Longest Journey wasn't the pinnacle of that amalgamation, but the game at least embraced the principle with pure joy and made a hell of a shot at greatness. It felt as if the story and the gameplay was fun for the designers, just how it is supposed to be.
Dreamfall, none. The few feather light puzzles were right out of the museum of antique adventure game challenges. Instead, fetch quests and cutscenes galore. No creativity in anything interactive, the adventure game elements obviously always just integrated with a sour facial expression, because "they had to". No story could ever save this. I played Dreamfall when it came out and only ever touched it again last year after the Kickstarter. I was pretty content with youtube videos in the meantime, because there was nothing to the gameplay parts. To this day, I'd rather read or watch these parts, a two hour movie much preferred to the eleven hour "game" experience.
TLJ told a rather straightforward narrative. As is the case with good adventure games, it felt player driven, the brain power of the player moved the game forwards. This is a feeling of immersion that will elevate even the most basic of stories, but particularly those with such loving detail as The Longest Journey. If the player doesn't really need his brain power any more - too many things are automated, made less complex or less difficult, controls are streamlined until the player doesn't communicate anything besides "do something with that" to the protagonist, inventory impoverished or removed even - the feeling of immersion in the story plummets. Which just wasn't understood in Dreamfall any more. The story is wanting because it doesn't find a reason for the player to even be there. I find it a failed attempt to 'streamline' the adventure game, and, yes, therewith a waste of a wonderful story.
TLJ I can replay every year, thank you very much. I will possibly never play Dreamfall again. There's a reason why the Chapters Kickstarter promised to retell Dreamfall's story in a more enjoyable, not interactive form.