Hugs.
You don’t need to experience any regret– at all- regardless of what you decide to do.
Princeton and Brown have more in common than different. You will have a boring professor at some point, regardless of which you choose. You will have an amazing seminar or lecture whichever you choose- and you’ll look back on it and think “This class and this professor changed my life”. You will have a roommate or suitemate who is an absolute slob who you can’t stand until you become best friends, and you’ll have a roommate or suitemate who you adore until you both decide “We’re good roommates, let’s keep it that way”. And you’ll take a class thinking “this is what I want to do when I grow up” and by the end of the semester you’ll know ‘I hate this”– and you’ll take a class just because it fits nicely with your schedule and you’ll end up loving it and want to do more, learn more, stretch more.
Please don’t talk yourself into regretting whatever decision you make today.