Are you from a small town and looking for big city job? Try both. Take a summer internship in a smaller town, or a semester internship in a town near to your university. Then take an internship in a bigger city and compare. The great thing about college is that your decision isn't permanent, and moving costs are low.
While entering an agency after graduation is a great choice, consider working in a non-profit or for a company. If you like sports look to working for a sports team. Don't just automatically look to a public relations agency either. Look at ad agencies that have client services departments or teams, they often have similar opportunities.
Don't just look at public relations internships. Look at media planning in ad agencies, or marketing internships. They aren't pure public relations, but they have similar tasks and will diversify your resume, setting you apart from others.
In college you have at least 6 semesters, and two summers of possible internships. Use them to build your resume and help narrow down what you might want to do after graduation. You will also have a diversified portfolio and skill set that can be applicable to more jobs then one.
Don't despair if you don't receive an offer for the coveted agency internship. Think if it as a way to expand your capabilities and become a more well rounded public relations professional when you enter the real world.
What types of experiences have you had that set you apart from your peers? What do you do to expand your portfolio and skill set?