Lisbon or Seville?

I’d stick with Lisbon if for no other reason than the ease of getting to it. To do it justice Sevilla needs more than two days.

I agree that Lisbon makes the most sense so that you don’t waste time traveling. And you need at least 4 nights for Seville. You could certainly spend 4 nights in Lisbon, too, but logistically Lisbon makes more sense for this trip.

I’d go with Seville. With only two days- or a day and a half after travelling- you can accomplish much more in Seville than in Lisbon. Seville’s main attractions are concentrated within a small and very walkable radius from its centre, while Lisbon is much larger, its sights more spread out, and is much hillier. Both cities are worth seeing, but I’d want to have at least four nights in Lisbon. As for connections, from Albufeira to Lisbon is about a 2:45 bus/train ride, while Seville is a 3:45 bus ride (although Spain is in a different time zone, so you arrive 4:45 later by the clock). That’s assuming you are travelling by public transport. If you’re driving it makes more sense to keep the car in Portugal. The biggest consideration is where you will be flying home from.

From where you will be, Lisbon would mean getting to either Lagos or Faro and a high speed train to Lisbon, in 3-4 hours.

Seville would mean a somewhat infrequent bus, but a number of options, from Faro in about the same time.

Lisbon offers more flexibility in transport, but in the end it depends on your interests.

Both excellent destinations, both a bit time-consuming to reach given the limited time you have available.

What time of year is this trip? Seville is quite likely to be somewhere between very hot and excrutiatingly hot during the summer. During the hot months I'd definitely choose Lisbon.

I love both cities, but I'd advocate for Lisbon because of its proximity to the Algarve.