FS is nice but needs a renovations. The rooms are old and the dining rooms usually full for lunch but emtpy for dinner.
Barrio Alto is nice but take a suite as the rooms are minute. I had to leave my suitcase at reception as I did not want to share the bed with it!!
I recently stayed at the Penha Longa Resort. It is in Sintra, 30 minutes from the city center. Great service, renovated last year and managed by Ritz Carlton. Superb spa, good golf (well maybe not on a romantic trip) and close to many historical areas. Had dinner in Lisbon, traffic in the evening is lite and taxis inexpensive. Worth a consideration.
Lapa is ok, a little stiff and over priced compared to other luxury hotels. however if you are booking a suite they have a penthouse one with a terrace on teh rooftop which offers stunning views.