i7 3770k is a better all round processor i.e. it is good in both light threaded and heavily multithreaded tasks.Fx8350 is quite good in some heavily multithreaded scenario like video encoding and 3D rendering with some rendering applications.If one has the money and requires processing power then i7 3770k would be more suitable.
Fx8350 is quite well priced though.Another thing is the low cost of 970,990fx motherboards which are quite feature-rich but cost good amount lower than Z77 motherboards.If somebody is running multiple VMs(say 4-5) simultaneously and doing intensive tasks in them fx8350 is a good choice much better than i5 3570k for visualization.Also the k-series intel processors don't have VT-d.
The sandy/ivy bridge processors are much more sensitive to frequency,have much higher IPC.If one is going for an overclock-able rig,i5 3570k+z77 would be quite good.i5 3570k@4.5GHz would be better than fx8350@4.7GHz in majority of tasks.People also tend to forget that the number of FPU units is only half as number of cores which should be fixed in Steamroller.For gaming all of them would be close at 1080p but with games which require more CPU power(skyrim,Civilisation 5 etc) the fx8350 would fall behind somewhat.
For specific things like virtualisation,encryption,rendering,complex kernel compilations,fx8350 is quite a valuable proposition.
Also users need to look at what kind of applications they use for the specific tasks that they do.A 3D modelling software can have many things well threaded while another 3D modelling software can have very few things like rendering as multithreaded and most other functions like applying occlusion or some other light settings as single or light threaded.
People use the word multitasking and multi-threading quite loosely.Here is just a real world example of multi-tasking:
Multitasking: Gaming while transcoding video
Each of these processors are fine and people can pick them depending upon their usage and requirements.