Having owned both of the cars in question (however both in manual) I can say I personally enjoyed the 280ZX more. The presence of air con, higher sound deadening, EFI fuel consumption, power steering, optional electrics and velour interior make it a much more practical and bearable daily. Whilst I did enjoy the 'first gen' styling of the 260z it was still a 2+2 which cops just as much flak as the ZX. I also love turning a car into an exception, where people will say 'I don't normally like *insert car*, but I like yours', so maybe I'm biased
I've always wanted to pit my ZX against an S30 of any sort, I can throw it pretty quickly around a corner and I've never ever had any understeer or had the back end become uncontrollable, call me a landbarge, I dare you!
As a daily, I personally wouldn't have a Z car at all as they're 2 door, relatively low and comparatively sad on fuel. The point I'm trying to make is that everyone is different, you just have to weigh all the facts up and choose one that is best for you, no Z car is better than another. One man's trash is another man's treasure!