It depends on what you plan to use your computer for. If you are planning to use your computer for gaming or non-intensive productivity tasks, the i7-10700K would be a great choice as it's a powerful 8-core CPU with a high clock speed and great single-core performance, which is important for gaming. The 5800X would also be an excellent choice as it offers excellent performance in multi-core applications like video editing and rendering and is also a great option for gaming. However, if you are planning to do heavy video editing or rendering, the 5800X may be a better choice as it offers 8-cores and 16-threads which is ideal for multi-threaded workloads. In conclusion, both CPUs are great options for gaming and productivity tasks, but it ultimately depends on what you plan to use your computer for that will determine which CPU is the best choice for you.