In general, if you want to go to grad school, especially for a PhD, liberal arts colleges are the best path. The two most important factors in being accepted to a PhD program are letters of recommendation and research experience. The more personal connections at LACs result in better LoR’s, while LACs focus on research with undergraduates. Whereas in most research universities, undergrads are generally relegated to lab tech works (at best), LACs allow and encourage students to establish their own research projects in the labs. Moreover, in research universities, undergraduates are competing with graduate students for the time and attention of the PI. Most undergraduates who work in labs at research universities interact mostly with grad students, or a postdoc, if they are lucky.
Although Brown is an excellent school, I think that, if you are looking to go to non-professional grad school, Pomona is the better choice.