I stayed at both the Westin and the Sheraton during the summer. Both hotels provided upgrades to a full suite. both provided full breakfast to Plats. Did not use the lounge aside from a short visit at the Sheraton, and checked in at the lounge at the Westin.

I preferred the breakfast at the Sheraton, but my wife thought that the Westin breakfast was better. Both were very good, in my opinion.

Quality of room? I preferred the Westin suite. Though the view from the Sheraton was of the twin towers. Westin suite I found was even larger than the Sheraton.

Location. For the first visit to KL, we stayed at the Sheraton. Did not find the location that bad. On the second visit, we were at the Westin and much preferred the location. From a tourists perspective, much easier to access a variety of shops, restaurants, people, etc.

I don't think you will find much to fault at the Sheraton, but if I go back to KL, I will definitely stay at the Westin.