I'll be honest. We've picked the colonial. I want to play into that.
All of the options are good. But in my humble opinion? Zuko and Aang are just too nice. So. My pick would be sanctioned broker in order to engage in some spycraft. But the other side of that, is limited diplomacy with the earth kingdom and its peoples.
And. We're going to need diplomacy in order to talk The Avatar and fire lord into not breaking apart families.
Another Major thing? The Dai Li. As far as I'm concerned? They're my grand prize. Elite earthbenders. Some of the very best, trained as spies and enforcers. Operation paperclipping them would be a coup. Pardon the pun. But ultimately, the fire nation gained an industrial advantage with firebending. However, with the invention of metalbending? We've seen, not only are metalbenders powerful on the battlefield, but being able to directly manipulate metal lends itself to all kinds of industrial uses. It's no accident that in the original timeline Kuvira's earth empire made such heavy use of metalbending. It's rare, and difficult to learn, but powerful. However to use it? We need earthbenders. And the Dai Li's own unique style of earthbending isn't too bad either.
All of which ties in neatly with bending revitalisation.
We see time and time again. That benders who incorporate lessons from other styles are powerful. Katara is a waterbending master, and when faced with another waterbending master far more experience? (Hama) Katara initially tries the standard waterbender counterattacking. But when that fails? She uses an 'earthbending form' to break apart the wave of water, shattering Hama's momentum. And it's a move that the older waterbender wasn't expecting and had no answer to. The other big example is lightning redirection. Firebending, but using waterbending principles to redirect the energy. Just as learning the other elements makes the Avatar stronger? Taking Lessons from other styles can make other benders stronger too.