Pci or Ethernet motion control?

[m_c]

If you want a system that's more plug and play, then you have to pay for it. And even at that, there will still be a certain amount of work you'll need to do yourself.

Personally, I'd go for ethernet, as it means should the computer fail, you unplug it, and plug in a different computer. I usually run cheap computers of ebay, which are generally reliable, but my laptop contains backups for all my machines, so should a computer fail, I can be up and running again very quickly (I do rely on my machines to make money, so I like to have contingency plans should things fail).

As you want it for a lathe, turn options are pretty limited. You have to consider what you'd like to do, and how you'd like to do it.
As much as it's falling out of favour and having some well documented bugs, Mach 3 is probably still the most comprehensive option for turn. Good turn support, and good turn wizards.
Mach 4 the last I checked, although now having turn support, I don't think the wizards were available.
However, with either of the Mach options, you have to pay for the license and suitable hardware, so it gets expensive. And you have to ensure your selected hardware option supports turn functions I.e. threading.

PathPilot looks good, but I gave up trying to hack it to run a test setup.

I use Dynomotion's KMotionCNC, however it has no wizards of any form (everything I do is pretty repetitive, but if I was doing small quantities of simple parts, I would switch back to Mach 3 for the wizards).

There are other turn options, but from memory the prices of the required hardware and software take a good jump from those listed above, and I'm having a complete mind blank as to their names!
Just remembered, FlashCut is one I was thinking of, but they don't publish prices.

The other option of course, are the standalone controllers, however you won't be wanting to transfer one of those between machines.