I tend to post everything of mine below a certain (arbitrary, likely inconsistent) length in a single catch-all work as separate chapters. This is mainly because I had a group of them before I had an ao3 account. Since then, I've kinda wished I broke it up differently, by theme or use or. Or or.

Which isn't exactly what you are talking about, but having done that, my strong preference would be for 2. A themed group with multiple chapters under a single work.