Hard to say because it's not yet fully operational- which kind of proves your point.
In an ideal world, or even a 1960s world, restarting production on a MKII Bronco would be ideal.
In today's world , starting a new program is just not doable for 200 airframes and the remaining Bronco airframes are at the ends of their fatigue lives and not a good airframe for overhaul.
That pretty much leaves us with the A-29. It's in production and it's a well done aircrafts
It's a little to biased to the CAS side and not enough to the COIN for Afghanistan IMHO, but in reality the USAF is never going operate from anything but smooth runways at a prepared air field in an Afghanistan anyway.
My bad
The AT6 is not yet fully operational
The A29 is