I would like to point out that TDP is not maximum or even average power, and it doesn't have much to do with a processor's overall power consumption. Most modern CPUs idle very frugally, and an office computer will spend most of its time at or near idle.
I agree that a laptop will overall consume the least power. One can approach laptop levels of power consumption with careful component selection - things like a low power M.2 drive (they're surprisingly thirsty), low voltage RAM, picking one of the lower-end chipsets, and an efficient (and not oversized) power supply.
Most contemporary computers are going to be so frugal that the difference between a high-end 8 core CPU and one of Intel's Atom derivatives will likely be lost in background noise.
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