Any areas where I should get a guided tour for ease such as skipping lines, insight, or interest such as history, food or wine tours. Any insight on which ones to use or avoid? April may time frame. 2 experienced travelers
If you are experienced travelers, you can explore all of these places yourself. I didn't get out to the Douro Valley on my trip to Portugal in 2018 because soon after I arrived in Porto, it started to pour rain the rest of my trip, so I didn't even bother trying to do my planned day trip out to the Douro Valley. I suppose a guided tour out there would let you drink wine and not worry about how to get back to Porto.
Sintra is very easy to do as a day trip from Lisbon by train. Take the local bus up the hill to the castles from the train station. Buy your Pena Palace tickets online ahead of time so you can skip the long lines at the entrance - or visit the Moorish Castle Ruins first (less crowded than Pena Palace) and while there buy your Pena Palace tickets, too.
I took "free walking tours" in each of Lisbon and Porto to get a lay of the land.
There are relatively few places with excessive lines - Pena Palace, Jerónimos Monastery, Tram 28 to name ones in the Lisbon area. The tour I took to Sintra did not take us into Pena palace - just got us there. But, it did walk us through the grounds at Quinta de Reguleira, which added a lot to the visit.
Food tours in Lisbon and Porto are a great way to find some highlighted foods plus get some history of the places. A day tour of the Douro valley was a good way to see a bit and not have to navigate on my own, so definitely don’t regret doing it.
Best way to see the Douro Valley is take a week long river cruise. Ours was wonderful.
We did a one-day Cooltour Oporto river cruise on the Douro River from Porto to Pinhao and back. Included lunch and tastings at two of the Quintas. They pick you up at your hotel in an air conditioned van. Highly recommend it if your time is short.