Question special

Many IMGs establish connections with US physicians through research. Given the limited opportunity for onsite rotations/observations, it is possible that one can have LoRs from research mentors but none from a clinical preceptor. What is the preferred ratio of research versus clinical LoR and how does the ratio differ between university programs and community programs? A secondary question is that how to choose between research LoR from a university hospital, a clinical LoR from a community hospital observership, or a clinical LoR from a hands-on private clinic rotation?