Surface, I largely agree with Downsview. However, I vastly prefer the design language for Downsview Park, York University, Highway 407, and VMC, once they're completed. My new favourite will probably be Highway 407 because it's magnificent and colossal, followed by Downsview Park for the nice greenery and the GO train running through the middle.
Subsurface--for platform level my favourite is Union, concourse is probably Don Mills though Downsview and Union are strong competitors. But, similarly, the photos I've been seeing of the TYSSE concourse levels are amazing...not sure if they'll unseat Union for platforms though.