Sheraton Lisboa is a nice hotel, if not exactly centrally located; downtown can be reached by at fast subway connection (10-15 minutes). The hotel has been recently renovated; try to go for the upper floors ( I have always been upgraded), with west view. Good breakfast at the lounge.Actually the downstairs restaurant has a good lunch buffet at very reasonable prices. I would rate it a better than average business hotel. The bar on the top floor has a fantastic view of Lisbon (west). Service can be a little erratic, though, but the view makes up for that.
Have a nice trip!