These days, feature-wise, it's probably somewhere in the middle. It had support for things like window functions long before they became available in MySQL and friends.

What it gives you over both is single-file databases which are easy to share, and in-process embedded mode, just like SQLite.

Unlike SQLite, it doesn't only support embedded mode, but can also be turned into a "server" DBMS that supports remote access from multiple clients (like MySQL/PostgreSQL). Hundreds of concurrent connections work fine from what I've seen. This can be changed in either direction at your discretion, the database file remains the same.