I wish I had a short answer for you.

We also use SmartThings. If I'm being disciplined, I add devices -- like bulbs -- to ST first and then use the Echo to discover them. For bulbs I used to use the GE Link but have had problems with them playing nice with ST. Cree Connected bulbs work well with ST. Separate from that, we use the TP-Link Smart Plug for lamps that don't use bulbs regularly available in smart systems Right now our "living room" group (created through Echo, not ST) consists of two TP-Link-connected lamps. Yesterday I hoped to add a ceiling fixture with two Cree bulbs but we ran into some fixture installation issues, so that hasn't happened yet.

Our condo is 90 years old, so we've had some hiccups with smart switches, which would be my optimal solution. For example, my master bath has four light switches -- two by the door that operate lights in half the room and two by the vanity that operate lights in the other half. Because there are 10 bulbs involved -- of varieties that aren't always available in smart bulb options -- I hope to ultimately have four smart switches, and then set up an IFTTT rule where if one switched is flipped, the lights controlled by the other three switches also turn on.

How have you tried to create groups? And what's your setup look like?