Help with Fidelity and BNP offer

I received an offer from BNP Paribas in New York to work in Fixed Income sales and structuring this summer. I also have final rounds coming up with Fidelity for Equity Research this summer and although I don't have an offer yet, I'm not sure if I do get an offer which one to take.
I absolutely loved everyone at BNP and 3 MDs have taken the effort to call me/keep in touch and try to convince me to come. I definitely felt that I would be exposed to upper management and learn alot as well as be in a really fun and diverse environment at a very stable bank.
However, I really like the culture at Fidelity as well and I know the pay is a bit higher. In the long run, I think no matter where I am I would like to end up at Fidelity or a similar buy side/investment management firm.
My issue is that I'm just a junior in college and really have not tried any side yet and would like to try both while I have the chance. Is it harder to switch from sell to buy or buy to sell? Also, do people find that the culture and people at buy side firms is as dynamic without all the fast paced environments at an investment bank? Another thing is what do you guys think about stability and opportunities or reputation at either firm?
Any info would help, I'm really torn because I've already developed relationships with these MDs and I want to make sure I don't do anything rashly. Thank you.