Assuming you have all of them, what order do you play them in?
I'm wondering because I plan of playing ME3 from the start again, and wondering what order I should play them for the best story reasons.
Citadels seems like it should be played before Thessia, because the events are too upbeat to be played before the Cerberus base. After Thessia, there's an urgency to get things done as fast as possible. Especially when TIM has the Prothean VI. Whereas if you did a good job after Rannoch, an upbeat gathering seems good since you just had a victory. Or you want escapist after things went bad.
Omega seems to be good for right after Cerberus attacked the Citadel, since you want to hit them back after the attack.
Leviathan? Not sure yet. Same with From Ashes.
I actually agree with you, OP. I'll elaborate on why I think this is the best for story reasons:
Omega should be played immediately following the Citadel coup. It simply doesn't make sense otherwise, and it MASSIVELY improves the pacing of the story. Serious. Plus, there's a certain dichotomy with it since Omega is sort of like the Terminus version of a dark Citadel, and an immediate retaliation against Cerberus feels right and is strategically sound since they would least expect it. Also, think about it - how did Aria obtain a Cerberus cruiser? You think she just sat on her ass during the coup? Not Aria. Unlikely. No, she attacked and hijacked a cruiser when Cerberus attacked the Citadel and tortured the crew (she admits this) for the access codes to Omega. If you do Omega immediately after the coup, it makes sense that Cerberus would not have changed the codes or noticed that a cruiser was M.I.A. After the coup, Cerberus missions die down a bit. Omega is a massive blow to Cerberus mobility in the galaxy. It fits perfectly and improves pacing dramatically.
From Ashes doesn't really matter, but I play it a bit after the coup because the Palaven - Tuchanka arc feels too urgent and important to sidetrack much during it. Specifically, I play it after Omega because with Omega taken from Cerberus, their mobility in the galaxy is dramatically decreased and it makes sense that the colonists would be able to push them offworld without reinforcements arriving.
Leviathan I space out. First missions between the coup and Rannoch, final mission after Rannoch and specifically after the Citadel. The final mission should be played sometime after the Citadel and before Thessia as Leviathan is a game changer for the war. If Leviathan was obtained early, the organic species would have had a massive advantage against the Reapers. But they don't. And so a late acquisition makes sense as there simply isn't enough time left in the war for Leviathan to really tip the scales much.
Citadel is best played immediately following Rannoch both for reasons of tone (you have just won a major victory, the last of the story. It is all loss from there on out until Cerberus H.Q.) and also for logical reasons. The Normandy just participated in a major space battle. It likely experienced minor damage. The reason why you go to the Citadel is to repair and upgrade the Normandy. Thus, it makes sense to place Citadel here for tone and story reasons.
The party, however, I play after the end of the game. Not as a real life epilogue, but because I actually favor a tragic ending in which everyone dies. And so, I headcanon the final party as either a final hallucination on Shepard's behalf or an actual shared experience on the behalf of all of the characters prior to passing into nothingness or the next life (similar to the ending of Lost, I suppose). But that's just me, it could easily be played before Thessia and still make thematic sense. But at every point after that, it doesn't.