I am going to Europe this summer and I plan to go to Portugal for at least a few days (my first and last stops are planned, but the bulk of the trip is open). I have never been and don't know much about it.

I am wide open for recs. I have 5-6 days to work with. Will be traveling to Spain afterward and flying out from there.

Lisbon seems like a must. Considering Porto or Lagos. Probably cannot do both.

TIA!

did Lisbon and Porto about a month ago so this is all still fresh

Lisbon:
We stayed at Hotel da Baixa and it was nice. Anything in that area is probably fine. Walk down to Praca do Comercio and see the Arco da Rue Augusta. Walk along the water at sunset, it's a big party and people seem to bring their own drinks and just hang out. It was really nice.
Take Tram 28 up the hill and see Castelo de St Jorge. Great views from up there. Don't try to walk it lol and get to the Tram early (by 9 probably? will still be a wait but not hours) Do the 24 hr metro pass and then take the train out to Belem Tower afterwards.
Lots of shopping if you're interested inthat

Restaurants we liked were Gin Lovers, Boa bao, time out market was cool but absolutely packed so we didnt stick around. Imprensa cocktail bar was cool but very tiny

Porto:
We liked Porto more. Definitely a different vibe, much more chill than Lisbon.
We stayed at NH Collection Batalha and it was a decent location. Relatively central. It's right next to Rue de Santa Catarina which is another big shopping street.
If you happen to be a harry potter nerd there is some interesting stuff around. Majestic Cafe and Livraria Lello both have some HP history you can look up. The university students look like they go to hogwarts too
Porto Cathedral has some good views, Igreja do carmo has a blue tiled wall that people seem to like taking pictures in front of
Walk across the ponte luis bridge and either take the sky thing down or you can walk it, going down wasn't too bad. Do a port wine tour while you're there of course. We did the Sandeman one just because they had an english tour that worked with our schedule and it was fun.

Agree with both assessments. Lisbon is so diverse, you can find all kinds of fun things to do. We've been 3-4 times, and still left a lot undone and unseen. To add a bit on Porto (only been once for 3 days, but would go again):

- All the port houses (to my knowledge) have English speaking tours, as the Brits are the number one consumer of port, historically. Graham's has the best views of all the port houses. Ramos Pinto had the best tour, in my opinion. We probably visited 8-10 of them, and after a while, they kind of blend together (and you might be walking unsteadily, too - it IS fortified wine, ya know).

- We stayed at the Yeatman Hotel, and happened to be there as a Michelin starred restaurant was putting on a special menu many-course dinner, and it was awesome. The hotel also has great views.

- We had scheduled a day cruise up the Douro River, but apparently, when the river is too high or low, they have to cancel it, as you can't clear bridges, or get through the shallow parts. They blame the Spanish, who control the water flow upstream, and they are livid whenever the nasty Spanish disrupt their economy. Interesting politics!