What all do you wish to do with this PC? How long do you expect the CPU to last before needing an upgrade? These are the major factors in deciding between specifically those two CPU's. Since the 3700X has more cores, it will be more suitable if you want to multitask, stream games, do video editing, or some other multi-threaded content creation. The extra cores also means it will stay on top of latest games for a longer time than the 3600X. Even current games can use 8-12 threads, which means some games, in some specific scenarios, can actually max out a Ryzen 3600X. A 3700X would last longer with such games as almost no current game uses more than 12 threads.