From my experience, AMD has always been cheaper than Intel so I've always defaulted just buying AMD. I mainly use it for gaming, listening to music, and watching movies.
Yea, AMD is cheaper for a reason. I dont know much about AMD socket compatibility, but if you can upgrade without changing to a new motherboard, AMD makes sense. Since you are coming from a dual core though, you would want to make sure the mb could handle a higher TDP hex or 8 core cpu, and if you could overclock.
If you are upgrading both cpu and motherboard, it makes no sense not go go intel for gaming. Get an i5 3570k and an z77 mb and dont look back. Even at stock it will outperform anything from AMD for gaming, and also has more overclocking headroom than FX. It will also use less power, and if you push overclocking to the max, the power difference becomes even larger.