If you drop out zwave and Insteon, it seems likely that some Nest/Zigbee/Thread option will be the low cost candidate for Summer 2016, and that could very well be SmartThings, in which case maybe it does bring Zwave back in with it. (Samsung is a founding member of the Thread group.)
The more specific you can be about your highest priority use cases, the better suggestions people will be able to make.
If you’re interested, here’s my project report on my own phase one: