What do you mean by "easy to overwrite"?
Although I personally prefer Foundation, they both have their benefits. Foundation is great for designers/developers as the default styles are very easy to override. Bootstrap is great for developers who don't mind the predefined styles - making it great for rapid prototyping but not so great for custom designs.
I liked the answer by @tracy_mills91. She has pointed out some really important points. I am adding my own personal experiences of using Foundation framework —
- Foundation gives FastClick.js out of the box. I was initially unaware of this library.
- Off canvas! One of the best components that's missing in Bootstrap. Foundation provides various different variants of Off canvas.
- Creating forms in Foundation is extremely easier than Bootstrap.
- GPU Acceleration — Foundation gives better animation support.
- CLI — A handy tool to create Foundation projects on the go.
I prefer Foundation framework for various reasons. Here are some of them —
- Less HTML bloating.
- CSS Components come with minimal CSS.
- Global Foundation script.
- Unique top bar with features like Sticky, Contain-to-grid and Clickable top bar.
- Finally, good support for Sass.