The dlcs ordered imo from best to worst.
For DAO
Shale - companion has dialogue through all the game, the quests are enjoyable and well done, fits the story the most.
Warden´s keep - Avernus/Sophia choice with interesting characters, companions talk, an extra ability, new info on darkspawn lore, also storage chest was needed.
Awakening - Predictable darkspawn plot, many new characters some are quite interesting, continuation of story. No romances, full of bugs that were never fixed.
Witch Hunt - dlc for morrigan-mancers, it gives closure for them. For everyone else just add some bits of lore, revisit areas, fight a new monster, and see Morrigan get away no matter what. Not my top dlc, specially after how hyped it was.
Return to Ostagar - Weak plot, nice ostagar scenery and bosses, cool weapons, closure with Cailan, excellent Loghain banter. More like a weapon pack with some story tacked on.
Golems of Amgarrak - Dungeon crawl, new mechanics and monsters to fight, the plot is weak but some lore bits are cool. No companions, warden goes all alone.
Darkspawn chronicles - Alternate universe slaughterfest, worth it for the fun factor of seeing what crappy choices Alistair made. Not worth replaying.
Leliana´s song - Boring story that Leliana already told you, does not affect the main game. The side-characters are bad, i liked the story better in my imagination.
For DA2
Legacy - good excuse to get out of Kirkwall, a lot of party banter, sibling interactions which was sorely needed, great final boss and new lore, interesting side characters too.
Sebastian - One of my favourite characters, and one the few sane LIs in DA2. His side quests are uninteresting and average, more of the same DA2 filler. His banter and convesations through the game however is good and add new perspectives to events, pretty much like Shale in DAO. Particularly worth it for female hawke LI.
Mark of the Assassin - plot only makes sense on act1, other acts is questionable. wyvern hunt provides variation from kirkwall, lots of party banter, lore bits, funny lines - in general is a light hearted dlc. Tallis gets more obnoxius as the dlc progresses, she becomes the protagonist and hawke the sidekick.
I cannot talk about the DAI dlcs because i haven´t played them yet, only watched a walkthrough to see the story content. Overall i don´t feel their price is justified, so i´m waiting for a price drop or that bioware somehow impresses me with further dlc, then i would be willing to buy these as a show of support.
I don´t know why, i am just not invested enough in DAI to justify spending more money on it. Here´s to bioware putting out something to change my mind.