I never used Eurail esims, but I can tell you that all national SIM providers in the European Union (wich is not the same with Europe the continent) + Iceland, Norway and Lichtenstein have to provide for free Roaming outside the “home” country in the other EU + EEA states. 

Here in EUR its not AT-T, its mostly as ´brand´ Vodafone or T-mob, Lycamobile is the cheap anywhere low-budget alt. I think it will depend if you only/mostly want to do call (many think that is very old-fashioned now-but its tipical USA-style, we tend to use app/whatsapp much more now) to ´the party´ back home or In EUR. We here know a thing about trains etc, but for this not or hardly-and certainly not for those from USA. IF you oinsist on wanting to know more, go to a broad forum like tripadisor-same Q will have been posted and answered there dozens of times and with the USA mindset taken in.