I am Portuguese, from Sintra, so I admit my advice is biased. First, I agree with others that you are trying to do too much in the time you have. The distances are short, but traffic in Lisbon is legendary and very anxiety-inducing if you are not used to it. Try to avoid driving in Lisbon if you can.
Your choices really depend on what you enjoy doing the most. I personally think that one day in Sintra is not enough. You will get to do the "typical" touristy things there, but much of the charm of this town is in visiting the less travelled sites, like Convento dos Capuchos, Quinta da Regaleira, and the Chalet da Condessa D'Edla. Also, last time I was there (last Spring), one of the locals told me that they are opening more of the grounds of the Palacio da Pena for horseback riding and hiking. So, you could either spend two days in Sintra and do the typical sites on the first (Castelo dos Mouros, Palacio da Pena and Palacio da Vila) and then the less visited sites on the second day, or spend one day there and skip the typical sites in favor of seeing the less visited sites.
For Evora, you need more than one day. It will take several hours to get there and the town and ruins are definitely worth more than a few hours. I agree that going from Evora to Sintra is going to be taxing. I would skip Evora and the third option on your list for at least this visit, and stick to the sites around Lisbon and north. Obidos would be an option, though I find it a bit touristy. It is a quaint walled town that gives you some of the flavor of the old walled villages you would see if you went East or to the Alentejo. Also, not far from Coimbra is Buçaco Palace and gardens, a luxury hotel in the midst of an old growth forest of cork, cypress and oak trees. There are hiking trails and the ruins of a Carmelite monastery accessible from the hotel grounds. To the west of Porto is the town of Aveiro, which is distinguished for its canals and colorful architecture--you can see it in a few hours if you have the time. As the medieval capital of Portugal, Coimbra is definitely worth visiting, and it's on your way north from Lisbon to Porto.