When I first got back into the hobby I started with postwar and newly-made traditional-size engines and rolling stock. As more and more scale, command control, highly detailed models came out, and I got over sticker shock, my tastes moved in that direction and now I hardly ever run or even display my postwar and traditional size models.
Then Lionel came out with the enormous Standard Gauge Hiawatha and I couldn't resist, even though at the time it was just a mantel decoration. Later on I bought some more Standard Gauge trains, built a layout with both 0 and Standard Gauge track, and now I'm in charge of a Standard Gauge museum layout as well.
I've also gotten into European trains - first ETS and then MTH when they started with their beautifully detailed Euro line. Never thought I'd be running the Orient Express or a tinplate Beyer-Garratt, but there they are.
And finally, I've gotten less and less interested in diesels and modern era rolling stock. One of these days I will most likely clean house and unload most of my diesels to make room for more steam/transition era stuff.