If you've been around HO for a while, you've probably run into Mantua at some point. Mantua trains for sale are usually those solid older steam engines that just keep going, along with kits that a lot of people cut their teeth on.
The designs are straightforward and built to last, which is why they still show up on layouts and workbenches today. You can find more in HO scale model trains when adding to a classic HO setup.