I stayed at the Sheraton Center City earlier this month and had a decent time. I'm a base memeber in SGP working on getting Gold, so obviously no upgrade for me. The staff was very friendly here - as I was greeted by name as I coming down the elevator (which is surprising b/c I only stayed one night).
Last summer my friend was in the Presidential Suite for a wedding reception. Fantastic suite, amazing 360 degree views of the Parkway and City Hall. In the spring/summer when the fountain at Logan Circle is on, it's quite a sight.
Once the renovations are complete this should be a pretty great place.