Alkylazide

Hi, first time writing here but I really need some others' opinions about this. First of all, I am an Asian junior year undergrad attending one of the universities in HK, majoring in chemistry. Our university selects a very limited number of students for fully-funded research internships and luckily I am one of them. And also I was super lucky to get three internship offers one from Harvard medical school and two from Scripps. (all chemical biology areas) To explain each lab's situation, Harvard one is a very new lab they just have two post-docs right now and accepting rotations for Ph.D. For the two Scripps offers, the labs are already well-established and have plenty of workforce to carry on research. I had a discussion with two Scripps professors separately. (I will call them Scripps Prof. A & B) The thing is they don't really need to sell themselves because they already got funding and tenure, but after realizing I am holding several offers, they do. Prof A said he/she can definitely write a ref letter for applying graduate school later, and Prof B said he/she usually gives intern students a co-author for the paper they publish which is true, I cross-checked. The problem is, in my situation, there should be a two to the three-year gap between the internship and the time when I apply for grad school. (It is a personal reason, and I really should) I shouldn't whine about getting several offers but I am still not sure which one is the best choice for later applying for a postgraduate degree.