Actually getting the nVidia GPU "really" switched off has often been a bit of a challenge.
Currently on a Lenovo P71 what I do is to have the nVidia-module not loaded (blacklisted or not even installed), load the "bbswitch" module and then execute "tee /proc/acpi/bbswitch <<<OFF" (and check with "cat /proc/acpi/bbswitch" if it returns "OFF"). Without doing this I noticed that the internal temperature when idle was a bit higher than what I thought it should be, so I must assume that otherwise the nVidia kind-of-GPU still consumes some watts even if the module is not even loaded/present.
NVidia on desktop "works" for me, but suspend/resume is a fiasco - one cycle and the graphics are never right again, flickering and crap everywhere.
Thx - I never even took into consideration Nouveau.
Sorry, I have 0 experience with desktop & suspend (I have 2 desktops, both of them using nVidia, but they're basically servers running databases so I have never made them go to sleep).
On desktop NVidia is good. On laptops I like Intel graphics. because I don't want to muck around with getting working drivers.