For my degree, there are two application cycles each year for MBBs firms: spring and fall.
Even before I started applying, I always had a slight preference for firm A over firm B.
During the spring cycle earlier this year, firm A rejected me pre-interview, after which I immediately resubmitted my application to firm A for the fall cycle out of desperation. Weeks after, firm B gave me an interview which led to an offer with a 2-week decision window. Believing firm A was out of reach, I accepted firm B's offer, since back then it seemed like my only chance of getting an MBB offer.
Months after signing with firm B, I unexpectedly received interviews from firm A in the fall cycle, and received an offer. After which, I networked with consultants at firm A and realized that it's a much better fit for me in terms of opportunities to work in the area I am interested in.
If I decide to sign with firm A and renege my offer from firm B, does this count as doing it out of bad faith? Is it bad etiquette? Should I do it? Was there anything I could have done better to avoid this situation? If I explain this situation to firm B honestly, will they put me on a permanent “do not hire” list?