We have some day trips planned during our stay in Lisbon such as Sintra, Fatima, Ciambra, and possibly Porto. Do you think it is wise to rent a car for these day trips or use public transportation? Thank you
Porto is a considerable distance from Lisbon and in my opinion too far for a day trip; unless you want simply arrive and then turn right around and head back to Lisbon. If you want to do an overnight stay in Porto it would be manageable and it is worth the visit.
I agree that Porto is too far for a day trip. Sintra merits and overnight, or two nights. If you mean Coimbra -- nice enough, but unless you have five or more nights in Lisbon itself, not worth the trip up there. I would rather have another night in Lisboa.