My "just work" devices have definitely been the Aeotec/Aeon stuff. Recessed door sensors and some older relays - been working for about 5 years now. Their motion sensors have been a bit slow but can be usb powered which is nice (prefer Zigbee ones anyway).
I do like the SmartThings devices too they seem well built - the old motion sensors just work and are fast. The single buttons are cheap and have been very reliable. I hacked the presence sensors per an old post on the ST forums and added bigger batteries for longer life.
Sengled bulbs have been decent - they don't mess with my Zigbee network like some other bulbs did.
I have to say our Zooz switches on our second floor (16+ switches) have been running great and by great I mean no issues - we have the "toggle" version. I have a really funky set of 4-way switch rules in which 3 switches are power only and everything works as expected.