Who is best processor ? I5 6th Generation or I7 with 3rd generation?

Best for what? What workload? what budget?

14-Cup Food Processor with Commercial-Style Dicing Kit from KitchenAid

If you are doing lots of tasks that strongly utilize multiple cores (lots and lots of video rendering perhaps), go with the 3rd generation I7. The hyperthreading will really benefit software that can utilize massive parallelism.

Otherwise go with the 6th generation I5. Most programs (including most video games) don't use many cores, so the I5 offers more than enough parallelism for these usages, and the sixth generation has more advanced instruction sets and better branch predicting compared to the third generation.