I have used Eurail passes for all of my trips to Europe. The European trains are clean and comfortable not to mention punctual. You can almost set your watch by their scheduled arrival times. In the rare instance when there is a delay, the time is clearly comunicated on board the train and at the station as well. Since we were going for three months, we purchased a three month pass which gave us unlimited access to first class coaches throughout Europe. (There are very rare instances where the Eurail pass was not valid - very rare).
We started by going to the Eurail site and looking at the Global Passes. Note that the pass is available in 33 European countries. The complete list is on the website. We chose to use the mobile pass (on our Phone). Watch their website well before your trip as there are frequent sales and you have a full 11 months to start your trip.
1st class!
We also chose to take advantage of the 1st Class pass. For the three month pass, the difference in price is $250 per person. It is well worth the extra! On some trains you get snack or even meal service at your seat. As you can see here, we were given complimentary bottles of water (and hand sanitizer as well as face-masks).
The coaches are generally less crowded than 2nd class (and quieter!). There are even some sections that are quiet zones.
The seats were always comfortable and some are airline styled seats with moveable headrests and reclining options.
Restrooms are typically located at the end of the coach and there will be signs on the wall at the end of the coach to indicate if the rest room is free or not.
More on actual train travel later... back to the Eurail pass.
One Country Pass
I should mention that there is also a one country pass if you think you will be only traveling in one of the 29 countries listed on the site. Quite frankly, it doesn't appear that a 1st class is significantly cheaper that the Global Pass and there is no long term pass (3 months). The longest unlimited ride pass listed is for 15 (consecutive) days.
Next: The Three Month Pass