I love Svelte. It's my first-choice web library these days. I will even use their online REPL to test out things like CSS techniques as a replacement for JSFiddle and the rest. Plus, I love the efficient code I get from their compiler, and how friendly Svelte is to web animations & graphics.

SvelteKit itself is quite neat. Getting SSR essentially for free, and having only a small learning curve for routing and the vendored bundler is just awesome. When I use it for dev, I typically turn on HMR and SSR, and I am extremely productive.