Why is the Spencer PDF specifically better than the competition for learners?
The text includes examples and exercises that compare analytical results with computer simulations, often providing simulation files for hands-on practice.
If you want Spencer's style of deep analog analysis, but need a legal, affordable, current book:
Review of linear systems and diodes. Use the PDF's search to find every "constant voltage drop model" example. Solve Example 2.4 on a tablet or notepad next to the PDF window.