I like to use bootstrap a lot, but I add my own styling ontop of the framework and add my own utility classes to make it function better. .mobile-hide etc;
I have always preferred doing it myself, but lately I have been leaning more towards frameworks. Mostly for the responsive grids, I don't need all the other components they have.
I like frameworks for having code already in place that I can edit, but I don't want the framework's existing design/structure to be limiting. I want to be able to modify it to fit what I want.
Depends on what the project calls for, alot of the time though customers want bootstrap so it is easier for them to customize so that is what i give them, for my own stuff i normally make from scratch.