The number of other students enrolled in your field of study shouldn't be a factor when you decide on your college major. That being said, there are numerous perks that come with how big or small your major actually is, as well as certain drawbacks. Whether you end up in Biomedical Sciences or Art History, there will always be positives and negatives, and you'll learn to appreciate your degree program for its own particular qualities. (Some colleges will even let you design your own major, but, no, "Bong Design" won't fly.)
Pro: Small major, small classes.
The farther along you are in your major, the smaller the classes are. It won't feel weird to have classes with 20, 15 or sometimes even 10 other people. You'll find that a lot of the time, these classes will not only be the most memorable, but also the ones where you'll retain the most information.
Con: Attendance is a must.
If there are only 14 other people in your class, your professor will definitely notice your absence. Attendance can often count for a serious chunk of your grade, so make sure you adhere to the professor's policy, whatever it is, and limit the times you're out. Even if your teacher doesn't care, your grades will thank you for it.
Pro: You'll make friends in your program quicker.
It's more than likely that you'll end up taking most of your main classes with the same people, and after countless group study marathons and projects, your classmates will become some of your closest friends. When you complain about a professor or a class, they'll understand completely because they lived it too.
Con: You'll eventually be stuck with someone you can't stand.
There will always be that one person you hate, regardless of your major. The difference is that in a small program, you will see them all the time — in your classes, during your professor's office hours, at club meetings and probably even at graduation.
Pro: Your professors will know you really well.
They'll know your name, your work ethic, your strong suits, and possibly also details about your personal life — like who you're dating or who you're friends with. It's inevitable, as you'll be seeing them all the time. But it's nice. When you need help, you'll know exactly which professor to turn to for advice.
Con: Your professors will know you too well.
Yeah, this pro is also a con. Just like they'll know your strong suits, they'll also know your weaknesses, and at some point they'll know you well enough to be able to see through excuses that might've flown with a professor who doesn't even recognize you. Plus, if they form a bad impression of you as a student, you'll probably still have to put up with them for a couple more classes. So try not to get on anyone's bad side.
Pro: Your professors will be accessible.
While sometimes professors will still want you to make appointments with them for office hours, they'll probably be easy to reach even if you don't have one. Sometimes your professor doubles as your faculty advisor, and popping into their office for a quick chat about your grades or an assignment you're having difficulty with isn't unheard of. Their offices doors are usually open and since they like seeing you take interest in your work, they'll likely happily help you out.
Pro: Professors are more accommodating.
If you have a lecture hall class, chances are that most of the slides and study guides the professor goes over in class will be available online. Some schools use Blackboard or their own proprietary platform to get material to students with digital ease. This gives you the option of going to class or watching the lecture later from your laptop.
Con: You'll be tempted to miss class.
With most material accessible to you online, you'll find yourself making excuses to skip class all the time. Why bother to show up for a three-hour lecture when you can binge-watch weeks of lectures from your dorm the night before your midterm? But paying half-attention to a lecture in your dorm and seeing it firsthand in class are two different things, and the most convenient option isn't always the most beneficial.
Pro: You'll always be meeting new people.
It's impossible to know everyone in your major, so you'll be seeing new faces regularly. You might sit next to someone one day and never see him or her again — not because they're not around, but because there are more than 300 students in the class. It definitely keeps things interesting.
Con: It's hard to make friends.
There will be classmates that you hang out with daily. You'll study with them, you'll eat with them, you might even party with them. But unfortunately, that's generally a one-semester thing. Unless your schedule for the next semester happens to be the same, you will probably not hang out with them again. You might see them on campus sometimes, but just in passing. This won't happen with all your classmates, but definitely with most of them.
Pro: You have more professors to choose from.
That's the thing with big majors. They need more professors to teach courses, so you as a student have more options of whom to take classes with. Ratemyprofessor.com will become your best friend, and remember: The earlier you sign up for classes, the better chance you have at getting the professors you want.
Con: Professors can be hard to track down.
You will definitely need to make an appointment to meet with most of your professors during office hours. And even then, you might still have to wait a long time to meet with them. Some of these professors teach multiple classes of more than 200 students, and if they all were to show up unannounced during office hours, things could get hectic.
Pro: You'll become a studying expert.
At the end of the day, your large major and your equally large classes will really force you to study material you have no recollection of your professor ever teaching. You'll learn all about marathon study sessions and how to drag yourself out of bed the next day for that 8 a.m. class you regret choosing. In a large major, you have to develop some self-discipline.