I'd pay for each journey in cash if possible. But that's difficult on the Metro as many stations only have ticket MACHINES which are often all totally buggered. Andante card is confusing to buy and use. It never swipes first time. English translation on machine is goofy. You have to swipe it every time you CHANGE trains which is obviously dumb. I thought Oyster was tiresome. Especially as the metro trains otherwise seem clean and modern, this ticketing system is about as reliable as Pete Doherty in comparison. It is truly pants. Don't let it spoil your holiday. When you swipe it and it flashes error, you just need to keep swiping it - 10 or maybe 20 times until you get the green light. Try faster, slower, turn it round etc. One bus driver passed his HAND past the machine first, and then the Anpante card. This seemed to work. Or it might have been a fluke.
If the machine don't work, staff cannot help. They'll just say your coins must be bad or you have no credit on your credit card. Insult/injury?
You have to make 6 journeys to get your money's worth on a daily Andante and Porto is so small, you'll probably not do it. We went to both art galleries, to the beach, across the bridge, up the funicular and still didn't get our money's worth. Swipe Swipe Swipe >Pants!.
Metro do Porto's Andante rail pass is unreliable and can result in tourists incurring fines of at least 50 euro! On the last day of our 4 day Porto trip we headed for the beach at Esphinho. A Sao Bento station officer helped us add trips to our Andante cards, validate the cards and suggested changing to the CP mainline train at General Torres station. We took his advice.
We took the 17:34 train from General Torres to Espinho, spent a few minutes there, validated the tickets at Espinho station in order to begin our return journey. We weren't concerned when the ticket officer came through our carriage because we had validated the cards. But his machine told him otherwise. We had a receipt for our ticket, but the contactless RFID system makes no imprint on the ticket so we had no proof. The officer insisted that our only option was to pay the fine. He had two police officers accompany us to Sao Bento station.
After being held for nearly an hour, we asked to speak to the ticketmaster's manager. A plainclothes man with no badge appeared and claimed to be the stationmanager. He agreed that we must pay, refused to give us his name and walked away. We asked a ticket vendor the stationmaster's name, he refused to answer. The ticket officer invalidated our tickets and took all of our money, so we walked to our hotel.
As a well-travelled tourist, I'm prepared for pickpockets and petty thieves, but I never expected that a rail company would have police backing to extract money from tourists. I had seen syringes from junkies at Espinho beach, pickpockets lurking around Ribena, and prostitutes at Trindade. But police were busy protecting CP from 2 tourists and their 3 year old daughter.
If you must use Andante, validate against all machines at every platform. Ask a station officer to witness. All Portuguese tourist businesses must provide for complaints. I informed Metro do Porto of my complaint in early October. I received one email which said they had forwarded my issue to the appropriate department, then nothing.
Avoid to go by car inside the old town center. In this moment all is upside down with the works for the construction of the underground.