I'm a fan of using a design system because then I don't need to think about the design and can focus on just getting the the thing to do what I want.
I also install tailwind to style everything.
My defacto design system to use is Carbon as it is pretty full featured for svelte and I'm using it for work.
I also use KonstaUI for personal projects and built a starter template for it. This is largely for applications that are going to be used from the phone.
I haven't used Svelte Material UI but one drawback is that it doesn't seem to be a full design system but rather expects you to pull in packages as you need them.