My husband and I visited Portugal in mid-October this year. We were fortunate to have 13 nights and visited Lisbon, Porto, and Coimbra. With only 6 nights, you have plenty to do in Lisbon with a few day trips: Sintra, Evora, and Coimbra can all be done in a day trip. Lisbon is best enjoyed slowly. The neighborhoods are so charming and our best memories were exploring the neighborhoods. You could easily spend 6 nights in Lisbon without a day trip and never be bored.
When we visited, it rained most days, so Sintra was a huge disappointment. It was so rainy and foggy, the colorful Pena Palace was muted. The wind was so bad, it wasn't really safe to visit the Moorish Castle. I wish we would have skipped Sintra and while I would go back to visit, it would only be in better (sunnier weather). We enjoyed Evora. We are big wine lovers so took a private tour to taste wine, visit Evora, and Monsaraz (a medieval village). It was one of the highlights of our trip exploring the Alentejo and an area that we would go back to.
If you don't mind being on the go and want to see a different side of Portugal, then your Option 1 is an easy transport option. We really liked Porto (spent 4 days there with a day trip to the Douro Valley). Porto is small, but packed with fun things to do. It is a bit more gritty than Lisbon, but has a charm of its own. If you like Port, then taking a food/port tour is a great way to explore the food and wine of the region.
Whatever you choose, if you are like my husband and I, you will want to return to this lovely country.