Markus, in my opinion, between the two schools in Vancouver, definitely recommend UBC. It's my alma mater but that doesn't cloud my judgement at all
Seriously, I think a big part of being on an exchange is the overall experience of a new place, not just academics, and UBC will offer much more in that regard. I have yet to meet someone who went to UBC and said they wish they'd gone to SFU instead. The other way, it's not uncommon!
I have a friend who finished her PhD in something-biology at UBC (shame, I should know really). I can ask her to get a contact for molecular biology there. She did her post-doc at Columbia and now moving to Waterloo, so she herself might have some opinion. Let me know!