Which is better a 5800x3d or a 12900k

It depends on your needs. The AMD Ryzen 5800X is a great processor for gaming and multitasking, while the Intel Core i9-12900K is a great processor for content creation and streaming. If you are looking for a processor for gaming and multitasking, the Ryzen 5800X is probably the better choice. If you are looking for a processor for content creation and streaming, the Intel Core i9-12900K is probably the better choice.