Alright, I really gotta pick an instance. Leaning towards ruby.social, since that's where a lot of people I follow seem to be landing. And my main motivation is: to have something to put on my slides at rubyconf in a month! Historically I've put my twitter handle there, but I'm not so sure now. At the very least, twitter and mastodon will be getting roughly equal billing.
I supposed sfba.social could be alright too, if I wanted to have a local feed focused on the place I actually live. But then again, there's a reason I'm not on nextdoor. :)