Flying from Porto Portugal to Barcelona Spain Nonstop

Any of them will get the job done. The only advice I have is to look at baggage requirements closely, and price to include what you will need. Ryanair for example, their base fare will not work for you, you need to upgrade, so just upgrade to what they call the Flex option (Allows a 20 Kilo checked bag, airport check-in, and a reserved seat). Do the same with other airlines to compare.

The biggest area people get caught, is that the bag dimensions allowed for carry-on are tight for the typical US bag, and most limit you to 10 kilos, which is on the light side of what most pack for a couple weeks. They do check, and you will wind up paying a hefty charge if over.

All else being equal, go with the best schedule.

Thank you for your quick and informative reply. We are only doing carry on as we are doing back to back RS tours. I will now check the size and weight requirements for carry on to see what will work for us.
Happy Traveling to you!

Of those mentioned, I've only flown Vueling (Barcelona to Vienna). I thought it was a pleasant flight. Helpful and friendly airport staff. The only slight negative would be no snack or beverage, but I doubt you'd get that from Ryanair, either.

I've flown with TAP and had a good experience with them. I've heard to be very careful to read the fine print for Ryanair since they are know for finding all kinds of ways to add in fees.

Of those you mention, TAP will have the best luggage inclusions without a fee. They allow an actual rolling carryon free. So, if you have a checked bag plus a larger carryon, it will save. Ryanair allows a large handbag without charging - one that goes under the seat in front of you. Iberia might have the same as TAP but haven't flown them within Europe.

I will just add, do not be adverse to checking a bag for a short direct flight. It is point to point, so little risk of losing a bag, and if you are over 10 kilo, you will need to check. Do not fall into the trap that "maybe" you can do 10 kilos without actually knowing how that will be done. Also realize that the perfect bag packed at home under 10 kilo may not be 10 kilo after a period of travel.

TAP does allow a cabin bag for the price. They also limit you to 10 kilo, which, as I noted, is tight for most of us traveling. With TAP, you also need to know what is allowed for your class of service, destination, and if your on TAP vs TAP|Discount. If you can't do the 10 Kilo, you will need upgrade and check your bag. TAP also does not fly Porto to Barcelona direct, at least on that day, you go through Lisbon which makes it a 4 to 10 hour flight with layover. Direct options will be under two hours.

Ryanair offers an upgrade to allow a 10 kilo carry on and personal item, which to my earlier point, figure out what you need, price accordingly. You need to compare Apples to Apples. Ryanair does fly direct on your day. Do be aware that Ryanair uses three airports in the Barcelona region, in this case you are flying into the main airport, just noted as "Barcelona" but if you see Barcelona Girona or Barcelona Reus, you do not want those for this flight, unless you are staying outside of Barcelona.

With Vueling, you will need to check. Only certain classes include a 10 kilo carry on bag without an upgrade, otherwise it is check the bag. Vueling flies direct to Barcelona.

Iberia includes a 10 kilo bag in the price, but also, Iberia is twice the price of the others easily. Again, over 10 kilo, you will need to check. Iberia does fly direct.

I've heard to be very careful to read the fine print for Ryanair since they are know for finding all kinds of ways to add in fees

To be fair, that applies to all these airlines, especially ones you have not flown on, this applies to US airlines as well anymore.

Just in the looking I did, I would probably opt for RyanAir or Vueling, if cost is not an issue Iberia might be an option.