I rather like the Sheraton in T3 - it's super-convenient and the rooms are clean and comfortable. The lounge is decent as well. The downside to Sheraton T3 is the price; it's usually amongst the most expensive of Marriott offerings around YYZ.

I echo other posters on the 4Points. It's conveniently close and perfectly adequate for a few hours rest.

I haven't been to the Westin in quite some time. I hope it's been renovated by now!

The other Sheraton (Sheraton Toronto Airport & Conference Centre) is nice enough with a decent lounge. The downside is that you're starting to get a bit further from the airport (about 3km). I've only stayed here once but I thought it was fine.

Furthest from the airport is the Delta which has good Platinum recognition, newish rooms and a good lounge. Downside is distance (about 5km).

**Note** There are two 4Points by YYZ. One is FourPoint by Sheraton Toronto Mississauga on Dixie Road. This one is OK, but the one I recommend staying at is the FourPoints by Sheraton Toronto Airport at 6257 Airport Road.