Supposedly, they have been renovating the Sheraton--I have not personally stayed there since around '97 or so.
The Westin used to be a D-tree, and is in Liberty Center. The Westin has a great restaurant (Fish Market) and some fairly nice rooms--however, I have yet to stay there since Starwood has been managing it.
OTOH, the Sheraton is at Station Square (nightlife, food, etc) and has some rooms with pretty nice views of the point and whatnot.
To a certain extent, it also depends on why you are in Pittsburgh, as you can pretty much walk to most/all of downtown/north shore (PNC Park, Heinz Field, et al) from the Westin, whereas you can walk to the southside from the Sheraton. If that does not matter to you, I'd go with the Westin. By a hair.
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Saving the world, one clue at a time.
[This message has been edited by ClueByFour (edited 02-25-2002).]