I used Svelte 3 for a fairly complex side project last year (rewrote it from React), and it's my favorite JS framework so far. I do wish the TypeScript story was better though.

I've also used Elm for another little side project, and it was super fun to learn, but it was a bit mind-bending at first.

I think Svelte is a fairly safe choice because it's actively developed and because it's not too different from Angular/React/Vue.

If there's any possibility that you'll have to hand this code over to someone else, I think Elm is a much less safe choice.

So, to echo tomerbd's reply: Elm for fun; Svelte for profit.