My tops are:
Nevada State Railroad Museum, Carson City, Nv. Lots of V&T and a really nice museum.
Local narrow gauge, steam weekends four times a year, come and watch for
free or minimal charge to ride the steam trains and the Mckeen car all day,
Illinois Railroad Museum at Union, Illinois. Out in the middle of nowhere, but
lots of stuff including a gorgeous restored Zephyr. Haven't been in 20 years
but it still looks the same online.
California State Museum in Old Town Sacramento. Amazing and this is the
Museum Tom Sefton donated his amazing standard gauge collection to.
Again, I have not been in several years, but there were big plans for this
museum.