I been to ER departments at a few hospitals in the GTA.(1)
Markham Stouffville Hospital's ER is one of the best one I had been to.
The staffs: doctors, nurses and the administrators are all really polite and courteous.
The wait was never too long... and the waiting area is quite spacious and bright.
Parking can be pricey, but the parking fees they collects are used as funding for the operations of the hospital.
This location is really convenient too because it is the final stop of VIVA Hwy 7 and Rutherford Routes. That make it accessible even for people that relies on public transportions.
(1) I was not at ER because I ate too much... I went with some family members