Bootstrap is commonly used as the go to framework due to it's popularity, and UI features. However, there is an issue of many websites using the same framework, and all sites look the same as a result of using bootstrap. Bootstrap can be heavily modified however, there is still certain aspects within the framework that will prove the template is bootstrap based.
On the other hand, with other frameworks such as foundation, which is basically a framework that relies template basics, it would be much harder to indicate that the website is using that framework.
I like to try and modify frameworks to my liking, so end users won't suspect that I am using a free framework.