I highly recommend Legacy. Mark of the Assassin has no relevance to anything whatsoever, and you have to endure Tallis. But the combat is fun, as are the puzzles. And there are some funny moments during the party, and with the banter.
Jaws and Descent are both fun. Jaws gives you a whole new area to explore, and Descent has some challenging combat and interesting lore. None of it is relevant to the plot, though. Well, so far anyway. Some of the Descent stuff might become relevant in DA 4. Jaws is pretty self-contained.
This is my preferred order for the DLCs.
Origins:
The Stone Prisoner (after both Redcliffe and the Circle Tower)
Return to Ostagar (immediately after The Stone Prisoner)
Warden's Keep (after all of the previous stuff and the Brecilian Forest, plus some Denerim sidequests)
Awakening
The Golems of Amgarrak
Witch Hunt
DA 2:
Sebastian's quest sometime during Act 2
The other two DLCs right before the endgame. First Mark of the Assassin, then Legacy.
Inquisition:
I do all of the main campaign, then the DLCs. First Jaws of Hakkon, then Descent, and then Trespasser.