The thing is that "learning C" means "I can write C code that compiles and might be full of bugs", whereas "learning Rust" means "I can write Rust code that compiles and has a small number of bugs". It's not apples-to-apples.
It's like saying "I found it easier to learn primary school maths than I did to learn a physics degree".
Definitely SQLite. Easily accessible from Python, very fast, universally supported, no complicated setup, and everything is stored in a single file.
It even has a number of good GUI frontends. There's really no reason to look any further for a project like this.