Arlo had a list here - but it’s a bit dated, maybe someone has newer info: New SmartThings Schema Integration for Arlo - Announcements - SmartThings Community
As to the other - deserves its own thread, but in short - I try to keep all my automations together, at a single point IF POSSIBLE. Some times that isn’t possible. I have/use a concept of system of authority. Basically, who’s in charge, what’s the BEST way to control that thing. Up until recently most of my stuff was in SmartThings, therefore most of my automations in SmartThings and I was moving the bulk of my automation from WebCore and SmartTlighting to ST Rules API equivalents. What about voice? Well voice routines had to be done in Alexa - no choice (You really think anyone uses Bixby? I know Samsung, you keep trying but stop trying to force Bixby on us in the western countries, you lost to Alexa and Google, K?). What about this other thing that doesn’t work with… (you’ll find a million of them) TRY to keep everything together - sometimes you just can’t. But it helps especially when it comes down to those times when you’re scratching your head asking, “why in the hell did it do THAT?”