Agree with Scholes & Empedocles on this one about MGH in this more middle part of the country.
Spoke at length with a # of pediatricians in Chicago regarding program reputations. Seattle Children's is very highly regarded (many call it #3 behind Boston & CHOP), nobody leaves it out as a top 10 program. The book "Walk on Water" (nonfiction about pediatric heart surgery & Dr. Roger Mee @ Cleveland Clinic) also mentions Seattle as widely thought of throughout the pediatrics field as a top 3. (No disrespect to Hopkins, Cincy, Denver, or Baylor).
I asked around quite a bit about MGH. It was not looked as highly upon here (few considered it in top 25 territory). The reasons I was told:
-it's a general hospital (or as MGH puts it, a "hospital within a hospital")
-they're in the shadow of Boston Children's...regional "interesting cases" would preferentially go to Boston Children's. Why go to MGH when one of the (nearly) undisputed top 2 is right there too?
Either way, I can't imagine a residency at either would ever hurt in the fellowship application process, and both would certainly help, though UW probably more so. Not to mention a pretty resident-friendly schedule.
Just my $0.02, based in large part on a # of attendings, fellows & senior residents I have worked with. Whatever...it's still the postings of an anonymous guy on an internet forum. Good luck with your decision making!