I would look at the colleges before I considered the dorms. Which one will get you closer to your goals?
I've gone to two different colleges, one while staying at home and the current one while staying in a single dorm room. For me, the deciding factor was that in my current college, I am better able to meet my academic goals and have access to more diverse courses and career related activities.
I like living at home because I feel comfortable, but it's true that because I'm on campus all the time, I have formed a network of people that I never would have met if I wasn't here all the time. I do have to say, it is way better to live in a single than a double. You can just shut the door and that says to everyone, "I'm done interacting right now. Lemme be." Vital for me since I get exhausted after too much social time. Sometimes I'm like, "Okay, I like you all but I'm going to go hang out with my fish now!" lol
Overall, it's about where you feel like you're achieving the most. It sucks to be away from your horses, but remember, it's only 4 years, you get summer and winter break and many schools have equestrian teams, if you need a horsie fix. I know it's not the same, though. As for bettas, at least in my school, they allow up to ten gallons. If you had four bettas with you, you'd be good. If you have more than that, maybe you could have friends help out? Good luck, it's a big choice.