I have four of the spying speakers, Google Home, Google Home Mini, Amazon Echo Plus and Harman Kardon Invoke powered by Microsoft Cortana. Whatever words in the English language are stronger than hate, that's how I feel about Apple, and their overpriced, overhyped lackluster products are not allowed in my house, so no Home Pod for me.
Amazon Echo has the widest skill set and seems like it gets functionality first. Amazon wants the Echo to be a centralized smart home hub and in addition to working with many third party vendors they pack as many of their own services as possible into it. Amazon Music, Prime, Audible, etc. As someone who was interested in becoming a subscriber, the main reason I got an Echo was for Audible support. I subscribed to Audible for a year on Thanksgiving Day, the last day of a special where if you became a subscriber you got a $50 credit to use toward an Echo device. Amazon had their Black Friday prices in place already so I got the Echo Plus for around $70 with the free Hue light bulb. I'm in the slow process of switching the whole house over to Hue bulbs, so it worked out great for me. I also like the Sirius XM support. The sound quality is noticeably better then the first gen Echo, which I never had, but heard it enough at other peoples houses to know it wasn't the greatest. I use the Echo primarily for smart home control, streaming Audible content, streaming Sirius XM and ordering stuff from Amazon.
Google Home is use for every day general use. I think they are focused more on their AI stuff that they raved about at the presentation thing last year and of course data mining. They don't have the extensive skill library Amazon has, but they hit all of the big names. As a user of Google Music to host my music library, not the paid streaming service, it's nice to be able to play music from my library on demand. I pre-ordered the Google Home and got it right away. In the past year+ I've seen the platform make great strides in terms of features and functionally. A lot of which I have no use for, but I'm sure others do. Since it pulls data from their own search results, if I have a quick question or something I've been wondering about, I'll ask the Google Home. The sound quality for music is generally mediocre at best, but spoken word is alight. Since the Google Home sits right on my desk three feet from me, I often use it to listen to podcasts, some of which I can't for whatever reason get with Alexa or Cortana while I'm on the computer. Since I've been using Google Music as my podcast app for years, it's nice being able to pick up where I left off when listening in the car or at work. I received the Home Mini for free when I pre-ordered the Pixel 2, given the size of the thing, the audio quality is not bad. It sits in the living room. I use Home primarily for streaming news, streaming podcasts, general queries and home control.
Microsoft Cortana combined with Harman Kardon. Cortana is by far the most limited of the three. Not many skills, not many supported audio services, but the audio quality is where it really shines. By far the best sounding smart speaker I ever heard, and it doesn't get crappy when cranked up to higher volume levels. I wish it supported more audio services and while pulling data from Bing isn't the end of the world, I'm just more used to Google. It doesn't support Wemo, but it does support Philips Hue. The Invoke is the slowest to respond, Google and Amazon respond almost instantly. It take about 8 seconds from the time I say 'Hey Cortana turn bathroom lights on' to the time they actually turn on. The main reason why I got this was to play around with it. No way would I pay the $200 list price, but at $100 the half off Black Friday sale, made it an easier pill to swallow. I'm glad I got it, if for nothing more then to play around with it audio quality is superb. The Echo Plus and Invoke sit next to each other on a nightstand thing by my window. This sounds lame, but it's actually pretty cool. I'll have one speaker play sounds of a thunderstorm, and one play the sounds of roaring ocean waves, and they mesh really well with each other. If I don't feel like listening to music or a podcast, I usually have them going like that.
I don't do much in the way of smart home technology. Like I said above the only platforms I use are Philips Hue for lighting, and to a lesser extent Belkin's Wemo smart plugs. Besides the basement and garage, I want all light bulbs in the house to eventually be Hue. Bedroom, bathroom, living room and the lone hallway light are all set. I have two Wemo smart plugs, one for my goofy lava lamp and one for a plug in light that sits over the stove. What makes switching over to Wemo more difficult for me is very few things are plugged directly into the wall. I have four APC battery backup units powering all of my computer and computer related hardware, and both entertainment centers in the house feature APC Power Centers.