AM3+ isn't dead at all, it's getting steamroller...and AMD has committed to the socket through 2015.
Additionally, anything you could do on an i5-3570k, the FX8350 will do as well or better for the most part...(itunes and skyrim being the outliers there).
I would say, if you multitask a lot, play games and do lots of multimedia type stuff, you're better served with the FX8350. If you mostly game, pick either one, the difference won't be much one way or the other.
If you intend to OC, go with the FX8320/8350...those will OC quite nicely.