Sigma 50mm 1.4 or Nikon 50mm 1.4g?

I do mostly portrait photography, so which lens do you think is better overall and in terms of bokeh? I've heard there's problems with AF on the sigma? Also, the Nikon 1.8g is obviously a lot cheaper than a 1.4, so do you think the 1.4's are worth all of the extra money? Is it really that much better?

I'm generally a big fan of Sigma lenses, but in this case I'd say go with the Nikon.
The Sigma 50mm f/1.4 struggles at the corners on full-frame Nikons, so if that's what you have, go with the Nikon (which still isn't outstanding at the corners, but it's better than the Sigma):

http://www.photozone.de/...ff?start=2

The biggest difference between the 1.8 and 1.4 is the bokeh quality (out-of focus backgrounds), which is more appealing on the 1.4. Otherwise, there's little difference, so if you're OK with the slightly more "noisy" bokeh of the 1.8, save some money.