I frequent St. Andrew station a lot as I work in the area, and it's always nuts. From 8am to 10am it's completely full of people trying to get to work in the Financial District, and the same deal from 4pm to 6pm with people heading home.
Although there are plenty of stairs to get up to ground level, the escalators are often out of service which really slows things down. Apart from that, it's just your standard downtown subway station.
Being so close to union, I like having the choice of two ways to get home (northbound to St. George or southbound all the way to Yonge/Bloor) if there is a problem on either line. This doesn't work for everyone, however, and when there are delays during rush hour (which are often enough, considering the construction at Union Station) it can get pretty crazy.
It's easy to get on the King streetcar in both directions, and the entrances are right beside the relevant streetcar stops which is handy when the weather is bad. read more