Hi everyone. .we have a country roads guided tour of Portugal end of March and are arriving in Lisbon one day early. We have tentatively booked a viator 5 hour guided private tour of Sintra which includes Pena Palace(2 hours for touring inside), and some time in the village. I have just discovered we have an optional half day with our tour company that includes the Portuguese riviera, Cascais, Estoril and the Quelez(?) Palace. For those having been, which one would you rather? Should add, we are not interested in touring Penas interior.
I much preferred Caiscais, Estoril etc. I did not enjoy Sintra nor the Pena Palace due to its crowds. Perhaps your private tour guide knows how to avoid those crowds.
If I understand it correctly the tours you mention are on different days, if that's correct you can do both, if that's not correct go to Sintra.
Sintra will likely be crowded but a guided tour makes it easier, if the weather is good you'll have good views from the Pena palace.