Loved, loved, loved the trains in Europe. We were in 8 countries and took the trains all trips except two. We flew easyJet from Rome to Athens and flew SwissJet from Athens to Zurich. Cheap and efficient.
Train advice-never buy first class tickets unless you are just too spoiled to book second class. We booked first class one time because the price was the same. The AC in the car broke down and we could not be moved to second class because it was full!!! It was very hot and especially so when we had a 45 min stop due to an accident. They did nothing to make us more comfortable, which is what you might expect from first class. We saw first class on all the trains and while the seats are a bit larger, they were not more comfy nor had more amenities. Second class had electrical plugs in most all trains so we were very happy to be able to charge up our devices. Many a time, we brought stuff and had a picnic on the train. Break out a bottle of wine if you wish.
We used the local subways systems heavily except in London. Their tube system was just too confusing and at the end of our trip we were just too tired to learn it, so we took taxis. We did not get great advance advice about the Athens subway system and booked a taxi from the airport into town. That cost us approx 40 euros. The train would have cost us about 20 euros had we taken the time to find the subway. Our hotel was near a stop. We did take the train back to the airport and it was great. Rome has an easy subway to navigate and most all the top sites are near a subway stop. We used the Paris subway extensively as we were not within walking distance of most sites. But it was very easy to figure out. London was hard in that London is so much larger, there were few express routes, most times you had to change trains. And although English is our language, the British were not helpful at all. We had an easier time with directions in Paris, where we spoke no French. We feel lucky we took the taxis in London , because we met two extraordinary drivers who talked us up a lot. We enjoyed that.
We took the vaporetto in Venice and loved it. Operators were so nice and helpful, we were blown away. My husband actually left his backpack on the vaporetto and got it back from lost and found a few days later. It had our camera in it so we thought it was lost forever. Company was so nice and helpful in locating it.