My new favorites are the Lionel aluminum CF hoppers. They're built strong yet still well detailed. I also like the mechanical reefers. The tank train and ethanol tank cars are my all time favorite. I need to add bolsters like Ed R.
Now, Lionel has auto carriers in their catalogs. They'll be scale length with operating doors? I wonder if these will look OK with my shorter MTH versions. The price looks large but at just over $100 street price, they'll give me the look of brass.