which one better for 1080p gaming?? i5 8400 vs 8600k vs 8700

Solution
With a 60Hz monitor it won't matter. Personally, I'd take an i7-8700 with a GTX 1060. A GTX 1060 is plenty for 1920x1080 at 60Hz. Since people tend to keep a CPU much longer than a GPU. The i7-8700 will have a longer useful life.

okay thanks mate!

 
You're far more likely to upgrade the GPU than the CPU [which might need a motherboard change to achieve] in future years. So you should get the best CPU you can at the point you are making that leap. Both the GPU's are excellent choices.