Sevilla Spain to Portugal

It would be helpful to know where in Portugal you want to go. We are also going from Seville to Porugal this May, and are taking the bus across the border to Faro and then picking up a car there, as we want to spend some time in the Algarve before moving inland and up through the rest of the country (we'll have @ 2 weeks in Portugal). If you want to go straight to Lisbon or Porto you might be better off flying...we found little choice in transportation options from Seville to the Algarve other then the bus, but there may be other choices for you depending on your itinerary.

The only way to get to Portugal from Spain is either bus or plane. There is no train that connects. From Seville you can take an ALSA bus to Faro. (it also goes to other cities) From there? I took the regional train (station is right in Faro) to Portimao, stayed one night in Praia de rocha, then took the regional train again to Lagos. I stayed in Lagos 2 nights then rented a car and drove for a week. I went to Sagres, (all over that area) to Evora, Lisbon and back. I was in Portugal for almost 2 weeks though.

If you only have 5 days you can either do the southern part of Portugal and enjoy yourself, or you can fly to Lisbon and do stuff from there.

In the Southern region, I loved Praia de Rocha in Portimao - beautiful beach town, very touristy; Lagos, another beach town, smaller than Portimao; Sagres was very interesting but I only stayed the night there to drive on from there. On my way back to Spain I stopped in Lagos (had to return the car) and then went to Tavira. Loved Tavira, very quaint town.
I went to the mountains, back down to Portimao for another night, then drove the coast and inland to Evora, a night in Evora then to Lisbon.
The southern part you can easily do all by bus and local train. Be careful of traveling on Saturday and Sundays - the taxi drivers charge 150% of normal fare on the weekend, and if it is a holiday even more!

ALSA is also the bus company for Sevilla-Lisboa. To compare flights, try www.skyscanner.com.

We are doing a slightly similar trip but driving since we have more time then you do. I would suggest taking a plane to Lisbon. There is so much to see and do there. I would go to Sintra (45 minute train ride) Belem (tram #15), Cascais and Estroil (about a 35 minute train ride) Going on the short ferry ride to Cristo Rei. I have used Rick Steves Portugal book, but I added the Lisbon TimeOut book too.
Enjoy!