You should get Trespasser, as it's a full epilogue for the game and provides the launching pad for the next game (you also get a more permanent ending for the Inquisitor and most of the companions).
Jaws of Hakkon is a new exploration zone (maybe a little smaller than the Hinterlands). It's the best area in the game by far, but it doesn't have a very heavy narrative (it's better than the other exploration zones, but it's not a story mission). There are quite a few quests, including a main quest that takes you throughout the whole zone (you're actually given a reason to cover most of it), as well as new items and a new ability.
The Descent has a fairly significant lore revelation, but it's not really expressed in any meaningful way (you're not told what its significance is, and you'll just leave with more questions than when you started). Other than that, it's just a big dungeon crawl, with some interesting but mostly empty areas (except the hordes of enemies, most of which don't respawn) and a couple mandatory NPCs that tag along and are responsible for most of the exposition (the companions do have some new lines, but nothing substantial). It does have some powerful new items, but no new abilities.
Nobody can say what you would find worthwhile, but the Game of the Year edition was recently released and contains all the DLC, so that may be an option if you don't mind waiting (it's full price now, but it will likely come down before too long, so you'd probably be able to snag all the DLC for less than the $45 it takes to get them individually).
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London et Bhryaen aiment ceci