With the Athlon X4 860K, you are getting Two extra cores, 4MB of L2 Cache (Compared to 3MB of L3 Cache on the Pentium), and a Faster base clock (3.7Ghz on the Athlon, 3.2Ghz on the Pentium). Plus, if you hook up the 860K with a R9 270X, You'll be able to play most games now at 1080p on Medium-Ultra settings.
With the Pentium, You are getting tons of Overclocking potential (Assuming you know how to overclock your CPU), which can lead to improved performance. However, since it only has 2 cores, I doubt its future potential at this point. However, hook it up with a GTX 750 ti or 760, and 1080p gaming is very possible.
Overall, it's really up to you. Personally, I would prefer the 860K, but both CPU's are great when hooked up with the right graphics card. In the end, it's all a matter of your preference and I don't want you to end up like the fanboys. Just waver your options and choose what you think is best for your money.
Hope this helps.