Newtown Square, Pennsylvania
I am making a trip to Amsterdam, Munich, Barcelona, and Rome from the United States and wanted to know the best city to fly into and out of based on most affordable price of the flights.
Try to fly into a hub for one of these airlines from the US (maybe Rome, Frankfurt or Milan Bergamo) then you can pick up a low cost flight to your other destinations. Remember too that it's relatively easy to pick up a rail link on continental Europe between cities, if you have time to spare. You can see a lot more from a train window!
Amsterdam Airport Schipholl without a doubt, the largest most efficient and probably the cheapest to fly to as well.
This completely depends on when you want to go, but usually I have found the best airport to fly into from the East Coast is Amsterdam out of the countries you listed.
Make sure to set some alerts on Kayak.com and other sites to get the best deal. You can set these for multiple airports and dates.
Also, you have to think of your itinerary. It sounds like you'll be covering a lot of territory on your trip by taking trains and/or buses and cars. For your trip, it might be smart to start in Barcelona, then take a train to Amsterdam, then a train to Munich, and then down to Rome where you could fly out. That way you're not doubling back on yourself at all.
Hope this helps.
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It really all depends on where you are flying from, when you are flying and for how long. When there is a huge conference going on in one of the cities prices go up. Also shorter stays are more expensive than longer stays. So there is not a real answer here. Also look at the possibility of flying to for example Amsterdam and fly back from Rome, sometimes this is even cheaper than a return journey. Just check out www.cheaptickets.com and spend an afternoon searching :-).
Amsterdam and Brussels are usually less expensive to fly into because there are more direct flight options there. We've flown out of John F. Kennedy International Airport and Hartsfield-Jackson Atlanta International Airport mostly.
Check out the links in Maria O'Dwyer's answer. Taking the train is great for views, but sometimes those cheap airlines can get you where you want to go fast and save you a lot of time.
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Amsterdam has probably the best connections anyway. So if you plan on flying in to any of the other cities you might have to stop anyway in amsterdam and catch another flight.
you might can use this to your advantage and book a trip for example to munich where you transfer in amsterdam. Now you can try to get a long overlay in Amsterdam.
If you want to travel between the cities, you might also want to check into train travel. To not miss a lot of the scenery...
When are you looking to fly? I'd say New York is probably the best bet for departure hub.