At idle, SSD is usually better (like you said if the SSD has proper power management, and that takes research to know).

Spinning platters are generally still better for power per gig/terabyte, because write time they consume less power than SSD.

I dont really look at drive power consumption, because even with ~10 drives running in my environment, a single cpu doing anything moderate blows away their power consumption numbers (I’ve tested, not that it was needed, heat dissipation alone makes it clear).

I have a ten-year old 5 drive NAS that runs 24/7, and it’s barely above room temp. Average draw is a few watts (the number was so low I put it out of my mind, maybe 5 watts - Raspberry Pi territory).

My SFF desktop is 12w at idle, with either 2 small SSDs (500GB each) or a single large drive (12TB). So much for SSD having better idle power.