What mobo and GPU - that will determine what data rates you can run, 16GB is normally good if your into other things, video and rendering, heavy office work, VMs etc then might, might give thought to 32GB
16 GB is more than plenty for gaming. 64 GB is even overkill for most content creators. Just Pick whatever 2 x 8gb or 4 x 4gb set of ram with the ddr (3 or 4) matching your motherboard.
What mobo and GPU - that will determine what data rates you can run, 16GB is normally good if your into other things, video and rendering, heavy office work, VMs etc then might, might give thought to 32GB