I was going to suggest Xiamen actually. I have a friend there who absolutely loves it, reporting clean, pretty tree-lined streets, good weather, coastal, and good salaries.
Nanning is really poor. Even among second-tier cities it is pretty second rate. It might be great for foreigners living there, but I think Chinese people look down on it a bit. My husband lived there for a short while and has a relatively low opinion of it, but then, what Chinese people look for in a city and what we look for are often not the same.
Like I mentioned in the other thread, Yunnan also suffers from the same problem as Guilin (perhaps even moreso). It gets loads and loads of backpackers as is, and every year a certain number of them just decide to stay, the trustafarians who can afford to work for nothing because they have no responsibilities in the first place. Then there are the retirees who just want a nice place to chill out and a decent respectable teaching job, and don't care much about the pay. Also, there's a lot of part time/under the table work, but the number of schools that are actually authorized to issue work visas are relatively limited. But the main issue is the pay. You would absolutely laugh if I told you how much I made working at a university in Kunming my first year there (back in 2003). An embarassingly small amount, I'm ashamed to even mention it!
Despite all this, we're planning on moving back to Kunming at some point in 2009, but that's mostly because my husband is a local and we have our own interests back there, that and the quality of life there beats Beijing any day. So there if money isn't really a prime consideration, definitely look into Yunnan, or Guangxi.
But check out Xiamen too, like I said, I have heard amazing things.