I have both tin and plastic Marx and, aside from some coupler issues, they both work well.
Prices on ebay have skyrocketed in the past few years, but I can still find some really nice stuff.
I also have a ton of Plasticville, various paper buildings, some AF and Lionel accessories, and a smidgeon of sctratch built stuff.... plus candy and cracker tins, out of scale Christmas decorations, and repurposed items. See, I'm running toy trains , NOT model trains and nothing is of any particular scale.