Basically Im looking for the "Best Value" (its never the most expensive one, but usually one notch lower).
What are you doing with the CPU? (Gaming, code compiling, video encoding, spreadsheets, data bases, VMs, a mixture, something else?)
Do you need a specific socket? (That is to say, are you planning on picking up a new MoBo also, or do you want a drop-in replacement?)
Where are you buying from? (US? Elsewhere? On-line retailers only? Live near a Microcenter?)
Do you plan on overclocking? (and do you OC to get max value, or do you actually take specific pleasure in the act of overclocking?)
It's really tough to give a recommendation without knowing answers to these. Off the cuff, the i5-4670k is great if you're mostly gaming and plan on OC'ing, if you don't plan on OC'ing you can save a few bucks by going with the i5-4570.