After having gone through the college search process with both of my children (junior at Cal Poly SLO, senior in high school waiting for acceptances), I can say confidently that it is very important to visit a campus you are thinking of attending. There are so many factors that go into the decision, but in the end, YOU have to LIVE there for four or more years.
@Gumbymom has provided a really good short list of criteria for a decision: Major? (does the school have a quality program in my field of interest?) Costs? (does the school fit my budget?) Have you visted both?(can I see myself living there for four or five years?).
If you have the first two figured out, time for a road trip.