The Sheraton is in a much nicer location vs the Westin. There's nothing unsafe about the Westin; it's just rather dead down there. On the plus side, the Westin can have nice views if you're on the south side of the building and it's a short walk to Harbourfront which is pleasant even in winter. There's a streetcar stop right outside the Westin that will get you quickly to Union Station which leads to many other transit options. And of course, it's a Westin so you'll get the Heavenly Sleep bed and the White Tea soaps etc.

The renovated rooms in the Sheraton are decent - nothing hugely special but they're nice enough. If you need parking, you're better off parking under City Hall. (The parking options near the Westin are rather limited and not worth the effort IMHO.) The breakfast in the Sheraton lounge is strictly a continental affair but it's adequate. The view from up there is one of the nicer ones in the city so be sure to take a moment of pause to enjoy it. And depending on where you really need to be, direct PATH access can be awesome. (But if you've never done PATH, you'll likely get a little lost.) During the week, at daytime PATH will be very busy. In the evenings it gets very quiet and on weekends it's a ghost town down there.

One potential downside to the Sheraton is that it's a large convention hotel. So it can be very busy at times depending on what's going on. The convention spaces below the Sheraton are some of the largest in Toronto. If there's a big one going on, you'll have to put up with large crowds, longer waits for elevators and more people in the various hotel restaurants. It's nothing insurmountable, but it's something to be aware of.