Agree with Stitch. The places that are better known tend to be the larger free or semi-free standing Children's hospitals with very comprehensive resources for children, i.e. all/many specialty docs in the same facility, large variety and numbers of complex surgeries, including cardiac surgeries, and being a Level 1 pediatric trauma center. In my opinion you can't go wrong going to any of these programs, because they all have a baseline clinical requirement and you will graduate as a qualified PICU attending if you do well there. This also applies to most PICU fellowships in smaller programs too, though. If a fellowship program doesn't offer all of the above factors I've described, its important to find out how they actually get you that experience. The Children's hospital in the same city/region, rotations at other hospitals, etc.
I will only specifically speak to my program and what draws folks here, Johns Hopkins. Fellows who rank us highly are looking for a large children's hospital with a PICU that includes cardiac and non-cardiac patients in the same unit, cohorted to different teams, but in the same unit. Which means you get equal exposure to all patients. We are the regional trauma referral center, so they are exposed to all kinds of trauma on a daily basis. We do large volumes of cardiac and non-cardiac ECMO (our NICU does not do ECMO, so our picu fellows benefit), and our faculty is split 50:50 between basic and clinical research, which offers trainees opportunities in both. There is an emphasis on doing a research project when you are non-clinical and learning the basics of research design and methodology, which will serve you well wherever you go. About half of our graduating fellows go to primarily clinical based settings, with the other half staying academic. Hope this provides some specific insights with regards to one program.