Pressure on the Return
Every player has a different return serve. Some people do the block in which they just let the racquet barely hit the ball and push it back, and some players like to use their return as their weapon by hitting the ball hard back at your opponnet.
What would I recommend is definitely both. You gotta mix up your game so you keep your opponents honest. The benefits of returning a hard serve is that you put pressure on your opponent and force him to rethink about missing his first serve.
I usually hit drop shots out of serves and I hit down the line and cross court. I always try to mix it up so my opponents are lost in a world of confusion.