Should I prioritize more RAM or faster RAM for my computer?

Go with more RAM first — upgrading from 8GB to 16GB is a huge improvement for multitasking and modern apps, while the speed bump from 2666MHz to 3600MHz only gives 5-10% better performance in CPU-heavy tasks on Ryzen (less on Intel). Even if the new RAM runs at the same slower speed, the extra capacity keeps your system from swapping to disk. Just make sure your motherboard and CPU support 3600MHz before paying extra for it.