Med school admissions is tough no matter where you go. But I feel like somehow half of my Wes friends are either currently in med school, are applying to med school next year, or were recently accepted to med school.
I think the lab research experience at Wes is a big plus. Literally everyone I know who wanted to work in a science research lab was able to do so (and, come to think of it, everyone I know who applied to / is applying to med school). A lot of students also either volunteer at the hospital or volunteer as an EMT to get some "clinical" experience.
I don't know much about Haverford, but my guess is that you can't really go wrong. They'll both be good for getting into med school. But if you're worried that grad students mean you'll have a tough time getting a lab position, don't be. There are tons of lab positions, and unless for some strange reason federal science funding is massively cut, competition from grad students won't be an issue