yeah, I usually use the boot-loader's "choose a snapshot to boot" menu option, but you can also use bectl to specify "boot $SNAPSHOT next time" with a flag to control "just once" (good for testing) or "I want to boot $SNAPSHOT as my default"
As for which, the most-recent or most-recent-minus-one (#penultimate 😆), something with a date prior to when you upgraded.

