I'm more invested into the Google eco system, however I've heard Amazon has a stronger skill set. But really I'd like to know which will do a better job of controlling Logitech Harmony Hub with NVIDIA Shield TV. Or should I forget the whole idea of voice controlling my TV and stick with the hard remote?
I'm a bit confused... are you aware that your Shield TV essentially functions as a Google Home now that it received the Google Assistant update about a month ago?
The remote (the 2017 version) functions as an always listening microphone.
It works even when the Shield TV is in standby/off mode. The main downside is that it doesn't have a built in speaker, so you need it connected to something that can play sound if you want to hear responses ("Ok, turning off bedroom lights"). There are workarounds (an always on receiver, or a USB DAC)
Harmony works fine with Google Assistant, but you do have to have slightly awkward commands (OK Google, ask Harmony to turn on the TV. OK Google, ask Harmony to increase the volume.) BUT, you can create shortcut commands using Google Assistant, so "OK google, turn on the TV" is translated to "OK Google, ask Harmony to turn on the TV."