As the sheer value, overwatch is the strongest one.
In reality P47 or UKF Strafing support\Hold the line.
Sector assault is hard-countered by the AA units, super badly. Almost pointless to use it, if there is AA around.
P47 tends to fly all over the map, instead of circling around the area, making hitting it down way harder.
UKF (especially AI planes) just delete inf, its like IL-2 strafing run, but with auto-aim and multiple hits. Tho they are also very susceptible to AA. But unlike overwatch\stuka-AT run, even if there is AA gun, UKF AI planes still might be able to wipe a squad or two before being killed, while Stuka AT runs only will be able to finish almost dead tank anyway.
And soviets are garbage
i just feel that factions that can build caches (pretty much all except okw) actually have an advantage over overwatch planes because 250muni is very expensive at any time