I've decided to learn D, and I'm wondering which standard library I should use. Should I use Phobos or Tango? What are the pros and cons of each?
Tango. It's more object-oriented where appropriate, it includes containers (like STL or Java Collections), it's got an active development team, it has more momentum (it may soon be incorporated into the official compiler), and it's got real documentation, including Learn to Tango with D.
It looks like Tango may soon be incorporated into Walter's releases.