Have a variety of serve returns. Your basic return should be a topspin (low to high) crosscourt. Mix in a few crosscourt underspin (high to low) returns to keep the ball away from the opposing net player and to float the ball at the feet of the approaching net rusher. Returning the serve as a lob is good when you want to break up the rhythm of a serve and volley team or to stop the opposing net player from poaching.
In a match, the sooner that you establish your topspin crosscourt return, the more effective the underspin return and the lob return will be.
Also, don't forget, when playing against a server that does not serve and volley (for example, a server that serves and stays back), the soft underspin crosscourt return can be used to pull them in, where they might not be comfortable.