Without getting too technical, here are the reasons why the Intel processor is the better one:
1. Lower TDP, meaning less heat and fan noise.
2. Better upgradeability for the LGA1150 socket.
3. Much stronger single and multi-threaded performance.
Don't believe that the FX is a six-core processor, as this isn't strictly true. Yes, it has six cores, but with only three FPUs (floating point units), it can only utilise a maximum of three cores simultaneously. The so-called six-core processor is, in practice, a tri-core.
In its favour, the FX is much cheaper, but that's because it can't match the i5 at all.