I have a bunch of the older X-10 stuff at my house, but it's not really supported anymore so I started looking at alternatives.
I currently have a Samsung SmartThings hub that I got during a sale for about $50. Switched out the thermostat with an Ecobee 3 with multiple remote temperature/motion sensors, which the SmartThings hub can see... which allows me to detect motion in the areas for automation. The great thing about the remote sensors is that I can see the temperature differences in each area, allowing me to make small adjustments to the dampers to try and balance the temps a bit better. It can also tell the fan to run a minimum amount per hour, helping with air circulation.
I've been replacing light switches with the GE Z-Wave plus ones that talk to my hub, and naming them so I can tell what's what. I've also grabbed some of the Google Home Mini devices so I can talk to the house. So when we walk in a can have a motion detection and automatically turn on the lights, or just say, "OK Google, turn on kitchen lights."
I use the "If This, Then That" app to automate some tasks... so for example, If it is sunset, turn on the front house lights. If it is 10 p.m. turn off front house lights.
I'm still playing with it, learning as I go... but it seems like the SmartThings hub and Home Mini are doing a great job keeping things integrated. No monthly fees, unless I want to tie my garage door app (Chamberlain MyQ) into my SmartThings hub. (Cost is driven by Chamberlain, not Samsung or Google.)
Lots of good info and smart devices out there nowadays... good luck with your search!
Mark