@JoeBobMackNeither of those is an easy question, yanno. But here goes:
1. I use 1st and 3rd limited, primarily, Maybe a slight preference for 1st because I like that it's easier to give my characters voice that way, and because I like unreliable narrator li, and I've written YA, where it's common. I've rarely used 3rd omniscient โ I prefer the immediacy of a limited POV.
2. Since I also write multiple 1st person, my answer is the same as for 3rd. I struggle with this, but my best explanation is , whichever character either has the most invested, emotionally, in the scene or the character who will be the most charged or affected by the results.
Though sometimes it's that, I've been with one character for "long enough" and it feels like it's time to switch. Or I've no idea what the scene is doing yet because I haven't written it, so just guess. Or whatevs.
Do I sometimes chose wrong in the first draft, and need to change POV when I revise? Yup. I rarely need to change the POV for the entire scene โ more common is, I guessed wrong when to switch. Usually how easy it is to do this tells me , changing is the right thing to do.