Should I choose 1×16GB or 2×8GB of DDR5 RAM?

Go with 2×8GB if 16GB is all you need. Using two matching sticks enables dual-channel memory, which provides more bandwidth and is generally better for overall performance than one 16GB stick.

A single RAM stick uses one 64-bit memory channel, while two sticks can use both channels at the same time. Dual-channel is technically faster, especially in games and memory-sensitive tasks, but a single 16GB stick may still be fine if it costs noticeably less or you plan to add another matching stick later.