So from what I can tell, the 3 maps of Lijang CTF require some pretty different strategies due to their layouts.
Control Center is all about area denial. Because there are so many small hallways and the placement of the flag, you want to be able to block off an area to either seperate the enemy team, or to secure their flag, or your path to cap.
This makes characters like Winston, Mei, and Reinhart pretty valuable. Because of the small space, Torb and Sym aren't as powerful here.
Garden is more about full offense. Because the enemy team can see the flag point from the spawn room door, this means you have less time than the other two maps to actually make your capture. The best way around this seems to move as a solid unit. Because of this open space, Torb turrets are helpful as they can reach a further distance, but are also subject to Pharah's long range.
This makes characters like Rein, Roadhog, DVa, 76, and Pharah pretty valuable here. Basically, you almost want a dive comp.
Night Markets is interesting, because there are a lot of small narrow corridors, but the open middle grounds makes traversing a challenge for more fragile characters. Plus, the shape of the Flag area is very awkward. This is the map where Torb and Sym seem to do the best, as there is so many varying levels of height as well as visual noise to hide Sym's turrets. Because of this Winston almost feels mandatory for cleanup.
Sombra, Tracer, Reaper, Junkrat, and Mei work pretty well here.
Note: This is all obviously just my anecdotal evidence, and is all from a console (PS4) perspective.