The i3 will likely be better for gaming. In fact, the edge is larger in gaming, since most games use at most two processes. I'll repost something I said in another thread:
Synthetic CPU benchmarks are not important; the question is how they'll perform in gaming (your primary use) or other tasks. Comparing the most current models on each side (that is, sandy and ivy bridge against phenom II and FX), intel has a substantial advantage in per-clock performance compared to AMD. Since games typically use no more than two processes/threads, the eight "cores" (a little complicated) in the FX-8150 actually don't offer any substantial advantage in most games over the two cores of a Pentium. That's why the core i3 is such a good performer--it has a relatively high clock on two cores (four threads with hyperthreading, but not generally relevant for gaming), and that's all you need for games. And it's why the core i5-3570k is a beast: it achieves very high per-core clock rates, AND those clocks do more per GHz than a highly-clocked FX or phenom II.
The synthetic bench, by contrast, includes all eight cores, so it scores the FX high. But that won't matter in most scenarios, and especially in games. In fact, Tom's rates the FX-4170 (four cores) higher than the -8150 (eight cores) for gaming on its hierarchy chart. Why? The four-core model can achieve a much higher clock speed per core, and those extra cores don't matter.
On top of all that, FX is not very efficient.
I like AMD, and even people who hate AMD recognize that it's good to have competition. So we're all hoping that Piledriver, AMD's next processor iteration, is a big improvement. (Trinity, the new AMD APU design, gives hope!) But for right now, you're better off with intel.
edit: here's a great chart from Tom's, which unfortunately doesn't include ivy bridge or bulldozer, but you get the idea:
http://www.tomshardware.com/charts/x86-core-performance-comparison/3DMark11,2761.html
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