I feel that I am qualified to speak about both large schools, and small schools. Although I attend a school with less than 3,000 students, I grew up in the same city as a school with over 40,000 and whose basketball team was a part of March Madness. Both are public state schools.
Pros of a big school:
1. Always something to do, whether sponsored by the school, an organization, or otherwise.
2. A wide range of people from all over.
3. Very few teachers will bother taking attendance, especially in the largest classes.
4. Bigger schools often have more money which means they can hire the teachers with the most prestigious degrees.
5. Sports, especially football will most likely be a big deal. The chances are better that you will be able to watch your team play on ESPN and tailgating will be like a holiday. It can be a lot of fun even if you are not a sports fan.