Enter your itinerary on this website and it will recommend which pass to get:
http://www.railsaver…
Choose from the three options of always railpasses, if more convenient, and if less expensive, based on your priorities. You may also want to double check the advice on other rail websites as sometimes the fares quoted by railsaver are more expensive than what’s actually available.

Train is fastest and easiest between Paris and London. Flying can be a little cheaper if you book early,although once you add transit to/from airports the costs become much more similar. An advance purchase youth fare will likely be better than the passholder fare on the Eurostar should you choose train, so I don’t think you’ll want to add a railpass day just for this trip. Oldlady, correct me if I’m wrong

For Amsterdam and London check the advice here:
http://www.eurotrip….

You can link to railsaver under “bookings” at the top of the page, or it’s part of the trip planner….

Railsaver is also limited to 15 cities…And when I take out the trip from amsterdam-london-paris, it comes up with a different result than eurotrip does:

Railsaver suggests the $445.00 Eurail 4 Country France/Germany/Italy/Switzerland 8 Day 2nd Class Youth Select pass + $299 of city to city tickets (this is not including the trip from amsterdam to london to paris).

Eurotrip when removing the same cities suggests a 15 Day 2nd Class Youth FlexiPass and
about $54.00 per person in city-to-city tickets.

What should I go for? Will this be sufficient if I do this and then book the amsterdam-london-paris segment separately?

This one is pretty much a toss-up. The total price difference is less than $100. That $100 will avoid the hassle of buying a ticket 7 times and buys you more flexibility for major changes to your travel plans as it’s good in more countries. You’re going to have to buy a ticket to cover the Polish portion of your trip in either case. Assuming 1) you’ll generally be taking trains that require reservations (which is almost as much hassle as buying a ticket) and 2) you’re unlikely to make any major changes to your itinerary, I think I’d opt for the cheaper package. If those assumptions are wrong, or you’re more comfortable with the idea of having more of your expenses paid “up front” then go for the 15 day pass. Support our sponsors and buy whichever railpass you choose from this site.