Bootstrap is a bit different in that it gives you a good base to work from. Also, for many more things than design hipsters would have you believe, it can be used pretty much as-is.
Angular.js, OTOH... I looked at it a while back and did not like just how much it forces you into its way of doing stuff.
Yeah... My personal experience with Bootstrap is somebody built a site using their grid system that I took over. My boss wanted to add a bar across the top but because all elements had class names corresponding to their position ("row1" etc.) the only way to do that was to rename every single HTML element. This would have been a two minute fix using vanilla CSS. If I had all the time back I spent resetting line-heights bulldozed by Bootstrap CSS I could have built an entire new site.
I use bootstrap quite a lot and I have no idea what you're talking about regarding the class names. That probably wasn't a bootstrap-related problem.
Overriding the styles is a bit of a PITA, but using the LESS or Sass version solves this.
Angular.js, OTOH... I looked at it a while back and did not like just how much it forces you into its way of doing stuff.