If your looking for a Nice Hotel I wouldn't look at Cass...
Sofitel hotel is great, right in the Michigan Ave area (has great lake/city views)
W Hotel sits on the lake (very nice hotel)
IF you want a nice hotel located in the center of it all.. Look at N. Michigan Ave hotels and some on Chestnut St.
If you want to go all-out. Get a room at the Park Hyatt
Also, The Drake Hotel
hmmm.. So many nice hotels in chicago.. But the streets I gave you should get you started. Let me know what you choose and I'll confirm its what you want (Since I live downtown on Michigan Ave)
WHATEVER YOU DO! Do not book at the Congress HOTEL.. I kid you not, the employees have been protesting for over 2years. . It's sad to see everyday when I pass by, how such crapy management is to let it go on this long..