I stay at the BWI Sheraton every week for the past 1 yr.
I have never stayed at the Westin.
This hotel is awesome. Service is too good.
Also, if you don't care abt the Points, you can get this hotel from Priceline for 70$ a night. Try for the 3.5* hotel in the BWI Airport Area and you will always get this hotel (A friend of mine who has stayed occasionally at this hotel has always got this rate and the same hotel).
I have got upgraded to a Suite 9 out of 10 times and the Suites are huge. Food is excellent.
Even after thinking hard, I do not have anything to complain.