I find foundation great for rapid prototyping, I can build a mockup in foundation in a few minutes and then iteratively improve on the design until it becomes a real product, as the name implies it's really a foundation to build on, it doesn't give you everything but it gives you 90% of what you need in a way that isn't restrictive.

Bootstrap gives you a lot more than foundation does, but I find it very restrictive, it's hard to make a bootstrap site not look like bootstrap (if anyone can point me to some counter examples I'd be interested). This is unsurprising since bootstrap was designed by twitter for a consistent look across their internal tools.

So my verdict is, for internal tools / quick hacks, use bootstrap. For mockups and real products, use foundation.