what will you be using your computer for?
i5's are generally the sweet spot for gaming because of their strong single thread performance in 4 physical cores.
the FX 8350 is nice also, but weaker than the i5 in many aspects, by comparison it generally takes an FX 8350 at 4.7/4.8Ghz to match the performance of an i5 at stock in single thread heavy applications.
http://www.bit-tech.net/hardware/2013/06/12/intel-core-i5-4670k-haswell-cpu-review/3
where the FX8350 can hold its own is in multitasking, it has 8 physical threads in 4 modules so it's excellent at parallel computing.
the i7 processors are pretty much just i5's but with hyperthreading, which is a feature that uses virtual (not physical) processing threads to parallel compute. They're expensive but they're the best.
Summary:
i5's for general use/gaming
FX8350/8320 for budget-ish builds, for multithreaded applications like 3D rendering and the like, and for enthusiasts because unlocked chip for overclocking
i7's if you have the money and want the best
also, generally buying later is better because prices will drop