Yeoman has the most active community with new generators being created at a rapid pace. Because of the momentum behind the community, you can expect good support and adoption for new tools and frameworks promptly after they come out.
Combining Yeoman and a backend framework such as Django, Rails or Laravel can create problem because the project structure of Yeoman may not be compatible with that of the backend project. It can be tuned to work but for small projects it can be relatively time consuming.
Anyone can register their package on Bower's GIT registry - on one side, this brings a lot of ease to developers, but on the other hand, this can lead to security issues because the packages are not signed.
To configure Grunt, developers need to basically write large files and configure JSON objects. While it's very powerful, the sheer complexity of it's configuration file may be a large obstacle for newcomers and developers that have not used any automation tools before. This may push them to