There are great variations of how trolls are portrayed, but it is not primarily a matter of national literature. I will be focusing on Sweden and Norway, where I know the traditions best.
First, we should note that trolls range in appearance from some that are quite human-like, to the point that they are able to move in human society and can only be spotted if someone sees that they have a tail, to some that are huge, monstrous beasts that really does not seem to differ from giants.
Trolls that looks like humans also tend to act quite human, in that they live in families, does things like keep animals, brew beer and marry, even if they live long and have magical powers. They can get along well with neighbouring humans, or behave as tricksters and thieves. They sometimes rob a mother of her child and place a changeling in it's stead, and they can also catch and hold grownups inside mountains. They typically live in forested areas. These traditions are strong in southern and middle Sweden (in northern Sweden there is a similar type of creature which are collectively known as "vittra"). I don't know how common they were in Norway.
The larger trolls are more monstrous in their deeds as well, and are often the type that would treaten to eat unwary travellers in folk tales. This type seems to be more common in Norway, but there are examples from Sweden as well. They tend to live in mountainous regions.
However, the difference is on a sliding scale and can be from story to story, rather than from region to region. We can take one famous example, Peer Gynt, as told by Ibsen, where the title character in the second act ends up in the hall of the mountain king, under Dovre. The king offers to let Peer marry his daughter Anitra and be made into a troll. There is no suggestion here that the trolls are in any way hideous: Peer calls Anitra lovely (Act two, scene five).
The story of Peer Gynt has parallels to the Icelandic Kjalnesinga saga, from the 14th century, in which the hero actually marries the daughter of the king of Dovre and has a son with her.
The most famous depictions of trolls from Norway was made by Theodor Kittelsen, contemporary with Ibsen; here is one example. A generation later, Swedish artist John Bauer similarly shaped the perception in Sweden. Here is one excellent example. Note how the Swedish trolls, while large, are clearly on a much smaller scale. These depictions mean that trolls today are mostly thought of as quite inhuman, even if they are not always outright monstrous.
The troll tradition seems to have been much less strong in Denmark, likely since the trolls were associated with wild and untamed areas, which were much less common there. I don't know much about Finnish or Sami traditions, even there seems to have been similar creatures to at least the more monstrous trolls.
Long story short: while there are tendencies that trolls tend to be more human-like in Sweden, and larger and less civilised in Norway, and there certainly are stories that clearly originate from particular regions, there are no hard rules. The biggest difference is probably that trolls in Norway tend to live in mountains, while trolls in Sweden are more associated with forests.
Sources
I found a good overview of different stories in Johan Egerkrans Nordisk väsen. I also checked Wikipedia in Bokmål, Danish and Swedish to see if there were significant differences or particular stories.
