Train?

It is most affordable to purchase nonrefundable non-changeable tickets 3 to 4 months in advance of your travel dates, at least for long haul trips, like Amsterdam to Paris and Paris to Switzerland. If you get a Eurail Pass, you will be required to make reservations for some of these trains, and sometimes the reservation fees can cost almost as much as a ticket bought way in advance. And those advance tickets come with seat reservations automatically.

You will get a number of responses here.
I've traveled over there 17 times and still never have gotten a pass because it seemed more expensive than point to point tickets bought on national railroad sites and not ones based in the USA.

I am of the opinion that Its better to buy individual point to point tickets on this site
for Amsterdam to Paris
Paris to Switzerland.
https://www.trainline.eu/

For Germany use the Deutsch Bahn site
https://www.bahn.com/en/view/index.shtml

....buy a pass and travel w/o reservations.... Except that most of the time you are required to purchase a seat reservation at an additional fee along with the pass. The French train limited the number of seats available for passholders so you cannot just jump on a train.

Here's a great discussion of the issues involved in passes vs individual tickets. Make sure you understand all his points before buying any pass: http://www.seat61.com/Railpass-and-Eurail-pass-guide.htm#railpass-or-point-to-point-tickets

amelia,

Even if you have a Railpass, you will still need to purchase seat reservations for the fast trains such as the TGV, as these are compulsory. Note that in France there's a quota on each train for Passholder reservations. Once the quota for that train is sold out, you wouldn't be able to buy travel on that train, even with a Pass. You'd either have to try and find reservations on the next train, or simply buy a ticket and forget the Pass.

If you'll be travelling in Italy you MUST have reservations as even with a Pass, if you're caught without valid reservations for the train you're riding on, you'll face hefty fines which will be collected on the spot!

See more about seat reservations here as well as on our rail pages for each country that you plan to visit. Trains in Germany and Switzerland don't need them, except for the Glacier Express or an overnight sleeper. Most passes are sold for a particular number of travel days (e.g. 10 days within 2 months in 4 countries). The best advance ticket discounts go on sale 3-4 months ahead for France and up to 6 months ahead for Germany but are not really a thing in Switzerland. Compare ticket costs when you have a pretty firm idea of the travel plan.

on the eurorail

Just to clarify, there is no such thing as "eurorail". "Eurail" is a marketing organisation selling rail passes and some rail tickets outside Europe, mostly in North America, but they do not run any trains. Trains are run by a variety of companies, mostly national but also some local companies. For example NS in the Netherlands, SNCF in France, SBB in Switzerland, DB in Germany and the high speed trains from Amsterdam to Paris are run by a company called Thalys.
For train times and buying tickets, go to the website of the company running the trains. Foreign resellers like Eurail may not offer you the full range of trains or the best ticket prices.

I advise you to read this website: http://seat61.com/Europe-train-travel.htm and the rest of this excellent website before buying anything.

In general....the pass pays for itself when you have multi-leg travel days with two or three changes. If you travel on intercity trains and not high speed the pass can be worthwhile. Committing 3+ months ahead is the least expensive option. Very few folks on this forum report having bought a pass.

I last bought a rail pass (5 day German Rail flex pass) in 2000, when I made my first trip back to Germany in over 10 years. After coming home, I checked point-point fares on the Bahn website and realized I had about broken even (and there were far fewer regional fares in those days). Since that time, 10 trips, I have always compared point-point tickets and regional passes with the cost of a pass before I go, and a pass has never been justifiable.

When I plan a trip, I price out the cost of each day of travel. The Bahn website is great for determining the least expensive fare for any leg. (Travel by U-Bahn, Trams, and Buses in VV is not shown, but this travel is not covered by passes either).

I list all of the days of travel, along with their costs, on a speadsheet, then sort them, descending by cost. Then I add a column for cumulative cost (i.e., day 1 is just the cost of day 1, day 2 is the cost of days 1 & 2, etc). Then I show the cost of a railpass opposite days when one is available.

For instance, for my next trip, for two people, days 1-3 are 58,90€ (Savings fare), 42€, and 36€ respectively. The cumulative cost through day three is 136,90€, or $146 at today's exchange rate (Oanda). A 3-day GRP, the least number of days you can buy, is $338 from RailEurope, so I would obviously lose money with a pass. The closest day to break even is day 7, where my cumulative cost is 256,60€ or about $274. Even with the current 20% discount for a 7-day pass, it would still cost $386, so I'm ahead with buy-as-you-go tickets.