I am currently doing my MA at Western, and I also did my undergrad here. I would say that it ultimately depends on your area of interest. Western is very strong in phil of science, but we also have a strong showing in the history of philosophy, even though this is not necessarily reflected in our rankings. We are well represented in pretty much every period up until the 18th century, including both Kant's theoretical and practical philosophy. Also take a look a the list of classes that are being offered next year and see if there is alot offered in your AOI.
That being said, Western has a very good MA program. The professors and other grad students are all very friendly and willing to help you. I never felt like I was a second rate student and there is lots of opportunity for both casual and professional interaction. I have heard this is not necessarily the case at U of T. Western also has a reasonable cost of living, so your funding goes further, and it also has a centralized campus, so your TA asignments are close by (I have heard this is sometimes a problem for U of T students, as they have campuses all over T.O., and they tend to give their PhD students higher priority).
I hope this helps with your decision. It would be better to talk to an MA student from U of T for more accurate info, as much of what I have reported is second hand. I can say that my experience at Western has been very positive overall, and it is a great place to do your MA. If you have any other questions just let me know, I would be happy to be of any further help.