I LOVE all of the differing opinions about W City Center and Lakeshore, and of course you are about to get mine as well
Having experience with both, I have to say that I like City Center much better, rooms are bigger and staff is considerably more friendly. I also like the neighborhood better (theater area). That being said, Lakeshore is a little closer to MI ave, although if it is cold out, you will want to take a cab either way. I did stay at the Westin once, and as far as 'touristy' goes, it is right in the heart of it.
On a side note, if you are Sushi fans, you MUST try Sushi Wabi on Randolph, YUM! And on the touristy note, I HIGHLY recommend a brunch at Ralph Lauren. On top of obvious tourist appeal, they have excelent brunch and service as well. I grunted when I was dragged there due to the fact that it seemed so very touristy and have happily returned on almost every trip. OK, I am hungry now, gotta go!!! Have Fun!!!