There is no "right answer" to your question, but there are a number of aspects to consider if you are hoping to go to Veterinary School. So, you need to go to a university that can offer you a solid preparation in all of these aspects:

First, no particular major is required - you can select any major that you are interested in and which reflects your abilities. However, most students major in some sort of Biology, since that major is pretty much in line with the vet school requirements and it also prepares you well. The required classes are: General Chemistry with labs, Organic Chemistry with labs, a year of Introductory Biology, Statistics, Physics, Genetics, Biochemistry, Physiology, and a year of English. Some schools also like to see a Business or Econ class. For UC Davis vet school, the average GPA is 3.5 the past few years.

Second, most schools require their applicants to take the Graduate Record Exam (GRE). Only the General Test is required. It contains sections designed to test verbal, quantitative and analytic ability. The higher your scores, the better your chances are of getting in.

The admissions committees look for applicants that have strong academic records and GRE scores. Strong letters of evaluation are also very important, so you need to get to know your professors as an undergraduate so that they can write informative letters for you.

Finally, the committee looks for strong motivation for veterinary medicine, maturity and good judgment, and volunteer experience.

Most schools, like UC Davis, actually state:
Substantial experience with animals, which should include working with veterinarians, is required. This experience should contain more than having had family pets. The requirement for animal experience can be fulfilled with 4.5-week equivalents (180 hours) if it includes relevant experience with types of activities that give an applicant an appreciation and understanding of the professions of veterinary medicine. This should include experience with several animal species so that the applicant understands the breadth of the profession. THE EXPERIENCE REQUIREMENT MUST BE MET IN ORDER TO HAVE AN APPLICATION EVALUATED BY THE ADMISSION COMMITTEE.**Other schools require 300-500 hours of veterinary medical exposure; many successful applicants have 2500+ hours.

So, your choice of undergraduate university should involve careful consideration of how well the school will prepare you for vet school. Are their opportunities to work with professors and get to know them well? Conduct research? Is the community one in which there are opportunities for volunteer vet work? Are the science classes rigorous? You need to feel challenged but comfortable at your undergrad school in order to do well, so visiting schools is a good idea. No matter how you slice it, you have to do well academically to get into vet school, so you have to work hard from the very first day as a freshman. Most UCs as well as CalPolys are going to prepare you very well for vet school admissions. Many students try to go to UC Davis for undergrad because that is where they want to go to vet school. But really, it is up to you. You have to be very proactive about your education and make vet school happen!

It seems to me that by asking this question as a 7th grader, you are well on your way! Good luck!

PS One more thing to think about: many people love animals and want to work with animals. However, vets have to also have to run a small business and have good interpersonal and communications skills (because after all, you have to deal with the human owners)!