Lisbon - mid Feb with time for Porto - 6 days

Can you give Portugal more time? Skip Algarve.
Evora is very worth your time. Porto is definitely a must see visit. We spent two weeks in Portugal and barely scratched the surface.

I agree with Suki. Skip Algarve on this trip and give more time to other cities like Coimbra, Sintra, and Lisbon.

For actual, day-by-day historical weather statistics (far better than looking at monthly averages), go to timeanddate.com and check February stats for your destinations. I'd check at least 3 years' worth, preferably 5. I've linked to Lisbon's data for February 2019. Spain is a large country with some wide weather variations. The central plateau (Madrid and surroundings) is likely to be cooler than Barcelona. The northern coast tends to be wet even in mid-summer. Andalucía is likely to be sunnier than other spots and warmer. But still, it's going to be winter, and days will be very short.

My opinion: The Algarve is way, way down the list of places to go in Portugal. Much of it has been grotesquely overbuilt, so you have to choose very carefully to find a place with some charm. And such a place is not going to be a quick trip from Lisbon. With only six days allocated for Portugal, are you prepared to spend any time at all visiting (in February) an area primarily known for beaches, golf course, British pubs, etc.?

I haven't been to Portugal recently so don't have current experience to back up recommendations for particular smaller towns, nor are you likely to have much time for them. Lisbon is a large city with quite a lot to see. If it is your first stop after an overnight flight, I'd certainly stay there at least 4 nights (giving you 3 full, non-jetlagged days). Whether that allows enough time for the desirable side-trip to Sintra will depend on how long your sightseeing list is in Lisbon. It's not a small city; it has interesting museums, attractive architecture, and hills that will potentially slow you down.

Ground transportation links between Portugal and Spain are limited and infrequent. There's bus service between Faro (Algarve) and Seville, an overnight train from Lisbon to Madrid, and some train and bus service from Porto up to Santiago de Compostela or other spots in Galicia. I'd tend toward that latter (northern) escape route if I was planning to see northern Spain. Otherwise, you can explore flight options on skyscanner.com. I believe there are flights between Lisbon and Seville (possibly also Malaga), which might be a good route if you plan to spend a good bit of time down in Andalucía--which seems like a very good idea to me for a February trip.

Picking up a rental car in Portugal and dropping it off in Spain is likely to be punishingly expensive. Once you're over the border into northern Spain, a car could be handy as you head east. In Andalucía a lot of travel is more efficient by train; a car is helpful if you want to see Ronda and some of the white villages between Seville and Granada. The AVE trains between Barcelona, Madrid, Cordoba and the major Andalucian cities are a great deal faster than driving.

If you want to see the Alhambra, stay on top of the ticket situation. Tickets regularly sell out months in advance, though I think sales may not be quite so rapid for February. The ticket-sale procedures can change at any time, but as of now I would expect all the February tickets to go on sale November 1. You should not have to buy immediately, but you should try to pin down the timing of your visit to Granada (assuming you want to go to the Alhambra) as soon as you can so you can take care of those tickets. That may mean pushing Granada to the beginning or the end of your time in Spain so the bulk of your time there can remain flexible, which I gather is your preference. I went through this myself in April, and it was a big pain to guess how many days I would want to spend in Ubeda, Cordoba, Cadiz, Seville, Ronda and Malaga--plus side trips from most of those places--before I reached Granada.

With only six days, I would stay in Lisbon, with a possible overnight in Evora. You really don’t have time to travel to Porto, IMO. And, in February, Porto will be colder than the areas of central Portugal. If you must see Porto, you could do four nights in Lisbon and two in Porto. But, it will take most of a day to travel there and back. I would skip it this time.

Only six days!
You need at least three full days to see Lisbon.
Also, in route to Porto, you could do Sintra or Obidos.

Porto is nice, plan on booking at the wonderful In Patio Guesthouse. It is the best B&B ever. Book early, it only has five rooms.

February is not great, it will be cold. The Douro River valley is nice, not sure you have much time to see it. You can take the train that runs on the north shore of the river or take a one day boat ride from Porto.

The Douro Valley will be a bit sad in February, without leaves on the trees and vines. I'd skip.
A day/ two nights in Porto is definitely worth it, however. More so than Évora for instance. Just take the train, it takes less than three hours.

I have a similar situation with Portugal except 8 nights the third week of February. I'm similarly hearing to skip the Algarve entirely and focus on Lisbon and Porto. After recently renting a car in Ireland for a week, I prefer not to rent a car again so we'll take the 3-hour train round trip to Porto mid-trip, but for us we can do 3 nights in Lisbon, 2 in Porto then another 3 in Lisbon. You might do 2 in Lisbon, 1 in Porto then 2 more in Lisbon or something, so long as you can have enough full days in Lisbon and a solid day for Porto. We plan on at least one day trip to Sintra while in Lisbon, maybe Belem, but otherwise not trying to see much else. Lisbon, Sintra and Porto are enough in a week, it seems, at least that time of year. But we'll avoid the tourist crowds at least.

thanks all for the tips - and we've decided to add a couple of days to Portugal on the front end as our plans are to go easterly over the trip and now planning to fly home from Paris over the 5 weeks there with a side trip to Normandy. Will also stay in Malaga for 10 days, Barcelona - 6 days, couple in Venice (fly to) train to Paris - a lot to plan for. Appreciate your feedback.
moraaly