I prefer to recommend the 2600X because I won't consider Intel at this time in order to encourage market competition and innovation. The more people do this, the better options we'll have in the future. However, it's fair to note that the 8600K is marginally better and the 8600 is cheaper.
But it's also prudent to ask:
What CPU and motherboard do you currently have?
What is your current graphics card. Your current expectations make a big impact on what you should buy.