Your question is something that I struggle with twice a month because we have an office in Nanning that requires frequent visits.

I usually end up flying down from Shanghai, but for whatever reason those flights are always delayed by at least 1 hour (even when taking the morning flights). Plus, it's a 3 hour flight on the way down (so, when taking the 1 hour ground stop into account, we're looking at 4 hours). I've tried every flight on the route in both directions; they all suck.

The only silver lining is that I have a 100% success rate of scoring either reclining exit rows or bulkhead aisle seats because nobody else who does the commute seems to know or care about getting good seats.

In any event, Shenzhen/Guangzhou are far better access points because the flight is quick (often less than an hour), delays are much less of a problem (1 hour tends to be the maximum rather than the minimum), and F only costs ~1000 (v. ~3000 in the Shanghai case). Shenzhen Airlines is my favorite, but CZ is also decent.

There is one flight per day between HK and Nanning, and I've taken it a few times. The problem is that costs 3x as much as flying from Shenzhen, and HK Airlines is a bad airline, even by China standards.

In closing, I encourage you to check out the Nanning thread (which I started) here, and PM/email before your visit; I will help you extract as much value as humanly possible from the experience. My prediction is that, like me, you will be underwhelmed/disgusted in some ways, but also get a sense of Nanning's bright future as China's gateway to SE Asia (its strategic importance to Beijing pretty much guarantees its long term success).