I stay at the Sheraton frequently (~50 nights/yr) and it is actually one of my favorite hotels (but mainly because staff now know me). It's markedly nicer than the Renaissance in every way I care about -- nicer bed, better breakfast, far better bathrooms -- especially if you get a junior suite or exec room (both pretty common upgrades for Platinum+). The number 4 tram outside is really convenient.

My other option in Zurich, in case the Sheraton is full (which happens, sometimes) is Kameha Grand. Much less convenient location, but interesting/nice, and often good rates.

The downtown Marriott is always more expensive than either, but nice too. It's actually a longer walk for me (since I otherwise take the tram to Zurich HBf then go down to Zug to client's office, vs. a 10-15 minute walk to HBf and then train).