Both use signal-based reactivity, both are heavily optimised at compile-time to ensure only the parts of your app that need to well change at runtime.

Vue uses single-file components, SolidJS uses JSX. That has a surprisingly large influence on how you develop with the frameworks, because it's a lot easier to create new components if those components are just regular Javascript functions, as opposed to being new files with boilerplate. But the boilerplate also provides some standardisation which might be useful for larger teams.

Vue has a much larger ecosystem. Partly that's about pre-built components and utilities, but it's easy enough to build things yourself in both frameworks, and SolidJS in particular makes it very easy to incorporate vanilla JS libraries when necessary. However, if you've got a weird setup, it's more likely that someone in the Vue ecosystem has tried out that setup before and either documented it or raised all the necessary bug tickets to get it working.

Personally, I really like SolidJS - it's pretty small, it's very simple to understand once you've got your head around signals, and it scales up well from single interactive elements on a page to complicated applications. (Specifically: one project I work on at the moment is an Excel-esque application where SolidJS handles both the UI and the underlying reactivity of the application. I have only needed to think about performance in a couple of cases, the vast majority of the time, SolidJS can handle hundreds of thousands of cells without issues.)

That said, if you're working with newer developers or on a larger team, or if you're new to web development yourself, I'd probably recommend Vue just because there's so many more resources out there for it.