Which school is best for an introvert?

Based on the way you’ve described yourself and what you are looking for in the college experience Penn is an unlikely match. Even as a CS major at Penn you will need to take courses outside of engineering (see: http://www.seas.upenn.edu/undergraduate/handbook/courses/ssh-requirements.php). Some of these may be of an “introductory” nature, although there are few, if any, simple introductory courses at Penn. Classes are relatively small, and if not, they are divided in small “tutorial” like sections. Like the other Ivies, student life at Penn centers around social interactions.

You may find what you are looking for in a large public university.