Of course since f3 is almost the same as bootstrap now, I think it's more about personal taste.
I use Bootstrap when
1. the default Bootstrap theme or a third party theme are sufficient
2. I don't need Foundation's better grid system
3. I'm using something other than Ruby (which for me is most of the time)
1. There's a specific problem that their better grid system solves. I haven't come across this yet, but am aware of it for when/if I do.
2. Client wants a highly customized Ruby-based site with no hint of the Bootstrap look
I like stuff with batteries included. Given bootstrap's momentum, it even has a plethora of design templates as well so you won't have a generic bootstrap looking site.
If I have a large family, I wouldn't really reason with myself saying "You know, it was an easy decision to go with a van as a coupé just doesn't really have enough space." Somewhat different purposes though one can see the overlap, which there is.
1) Comparing two similar CSS frameworks is different from comparing two very different classes of automobiles that are visually different enough to figure out in less than a second.
2) Not many non-designers look at, let alone even experiment, with enough CSS frameworks for this to be a simple and trivial choice.