SmartThings. I have it integrated with my Echo and Dots so far.
The online community has made this probably the best HA system out there IMO, despite the ST cloud infrastructure growing pains. ST says they're concentrating on beefing up the infrastructure and this is slowing down official enhancements. The ST Engineers/Devs have learned to stop promising features/updates on the forums because they can rarely deliver on time, which ****es everyone off. But the online community devs have created some smart apps (CORE, AskAlexa, SmartTiles, etc.) that have greatly enhanced what you can do on the platform. Hopefully someday ST will build those enhancements into the official platform.
I think ST is a good mix for slightly technical folks all the way up to developers/engineers. You can get as crazy as you want with it.
I initially bought into ST to control my chicken coop door and have slowly started adding relays/dimmers to my light fixtures controlled by motion sensors. I usually buy SmartThings devices or even some compatible Iris branded devices from Lowe's when they're on sale. The water leak sensor in my basement has already saved me twice so I'm pretty happy even though the ST platform has glitches now and then. It was hard to break the wife from the habit of using light switches as they're not really needed with my setup, but over time she's adapted ok. She still grumbles when there's a glitch with the system now and then.
I have an automation to alert us over the speakers when there's a water leak in the basement, it also sends app notifications and a text to our phones.
I have automations to turn on lights in several rooms when motion is sensed, and to dim certain lights at night, like when I go downstairs for a snack or to the bathroom.
I have an automation/SmartApp to control the color of the Osram Lightify lights on the front sidewalk, different colors for different holidays.
I have automations to open/close the chicken coop door when I want. There's even integration with the D-link streaming camera in the chicken coop.
I have an automation that opens/closes the garage door as we depart/arrive and turns on the entry lights. This one also send a voice notification over speakers connected to the system.
I have a few Aeotec remotes around the house that control lights/switches or perform some of my automations with the click of a button.
I have a few open/close sensors on a door or two to let me know if someone has opened a door.
I have my Ecobee thermostat connected but let the Ecobee control things as it's pretty rebust, but there are some community Ecobee device handlers and SmartApps that take it to a whole new level if you need more functionality.
Lot's of reading here:
https://community.smartthings.com/