This is entirely dependent on what you do and what your goals are. Generally, I think it's better to be really good at one thing. However, this wouldn't hold

This is entirely dependent on what you do and what your goals are. Generally, I think it's better to be really good at one thing. However, this wouldn't hold true in certain roles (think Enterprise Architect, Systems Consultant, ...). In different roles, it can be extremely valuable to have a broad, not necessarily deep, understanding of the various parts in play. What are your objectives?