3 days in Barcelona or Lisbon?

That's a tough question, because they are both great cities and deserving of your time. I haven't been to Lisbon recently, but I think you'll find Barcelona more intensely touristy in some neighborhoods. Entry fees are probably going to be higher in Barcelona, and I think you'll find more sights in Barcelona that really require prepurchase of tickets, because the ticket lines are horribly long. It's hard to put together a really efficient sightseeing strategy for Barcelona because all those tickets are timed, and you have to guess on the timing when you want to go from one to another. I'd feel more comfortable with 4 days in Barcelona because of the challenges, but I know some people squeeze it into 3 (or even fewer--eek).

Lisbon is a lot hillier than Barcelona. I've read here of lines at sights in Belem, but I don't think there are as many tough-to-visit sights in Lisbon.

Both cities have good side-trips available if you want to get out of town. Sintra and Cascais are easy from Lisbon. Girona, Figueres and Montserrat are among the most popular side trips from Barcelona. Those are just examples.

I went to Lisbon for the first time in October and loved it. Stayed four nights and it was not enough.

I am scheduled to go to Barcelona this coming October to take a cruise. I am nervous about the crime rate from what I have heard and read. It is not just the pickpockets. Violence is now being used against tourists to rob them.

Police are allegedly overwhelmed by the situation.

I have already made a lot of plans which includes booking air, other wise, i might change my cruise leaving from another port.

Do some research about crime in Barcelona available on this forum as well as youtube videos.

But in saying all that, I do hear that Barcelona is beautiful and interesting.

Have you been to Spain or Portugal before? We were in Barcelona and Lisbon last fall, and spent several days in each place as book-ends to the cruise. I would recommend adding a few days for both, but if I could only do one, I would likely pick Barcelona by a hair. I think either is a home run for lots of things to see and do, so there is no "wrong" answer. We're "active" travelers, so walked all over the place, and I can say that Lisbon was the tougher of the two because it is so hilly and has tons of cobbled streets. But it was also packed with lovely places to eat, and the bus & train system was easy & useful, and the Uber we got from the hotel to the airport was efficient and CHEAP.
If you have never been to Spain, though, I think it REALLY flourishes later in the day, so on a cruise, you might miss that big part of their culture if your ship is only in port from 8am to 6pm. You might have an overnight or two docked while on the cruise, but if not, I think having a few late evenings in Barcelona to truly experience their culture is important.

I mulled your question for several days... Two cities I Truly Love....and it took me back to my expectations and realizations of both cities.
I won't bore you with the details.... but my recommendation is Lisbon.

Tom B - the o.p. is interested in staying before or after the cruise. We stayed in Barcelona for 3 days after our cruise. Had a day stop in Lisbon on the cruise. Either will be good. My wife speaks both languages so I anticipate a return trip !

Lisboa
I have spent 10 days in Barcelona
I have spent 10 days in Lisboa
Never intend to return to Barcelona
Have another 10 days of activities planned for Lisboa

@stephen - I think I could have made my point more clearly.

The reason I voted to spend days ahead of the cruise in Barcelona and not Lisbon (I would suggest both if at all possible), is that I find Spanish city life REALLY shines in the evening and into the night. Cruise ships usually arrive in the AM and depart around 5pm, so going all the way to Spain for vacation and missing the wonderful times in the evening would be a shame.

The OP may have one or two ports where the ship stays overnight, so if that is the case, there is an opportunity for enjoying the Spanish night life at that time. In that case, it really is a "can't lose" situation as either city is worth the time and it will be nice no matter how it is decided.

Lisbon - much more relaxed yet vibrant, safer, a distinct culture, budget-friendly, kind people, incredible food!

I would prefer to stay the 3 days pre-cruise as opposed to post cruise. You have a chance to get over jet lag and be fresh for the cruise which can be physically taxing with the many shore excursions. At the end of our Med cruise, I was happy to just go home. Also, this gives you the chance to buy any necessaries that you may have forgot to pack or find that you need before embarking the ship. And IMO, the food in Spain is better.