Small group content offers a more intimate setting for you and a few friends (or strangers with potty mouths) to tackle an instance. Because there are so few of you, each player needs to pull his or her own weight and become a hero. These runs tend to be less stressful and far more accessible to the game's population.
On the other hand, raids offer the most challenging content in the game. A raid requires all involved to be geared up, skilled, and knowledgeable in the ways of fight patterns. Participating in one can feel downright epic, especially when you consider that you can see content that many players will never witness.
So let's put it to a vote! Which do you prefer: raid or small group content?