Learn a lot about one thing or a little about a lot of things?

Should Custom Software Developers be Generalists or Specialists? 

Spoiler alert: " I think the answer is that I need to be both. There are a few things that I need to know deeply. Deep enough that I am prepared to solve complicated problems that my teams encounter in that technology. There are many things that I know broadly. I need to know enough about them that I can leverage those technologies to solve a wide array of problems my team might encounter throughout the life cycle of a project," Eric Potter writes.
 
True for testers as well.  I want to know enough about everything that I can point junior colleagues in the right direction when they have questions.  But I also want to be an expert of at least a few things, so that I can be useful in solving particularly arcane, tricky problems.