I do S scale American Flyer; for that genre, I consider the 1950's era the cream of the crop. Detail is very good, and modern track is more realistic than the original stuff I use. That said, I would not recommend it unless your pockets are deep---figure $25 per car for average rolling stock, $50-$75 for more rare. Locomotives from the steam era and running on ac are as cheap as $30 plus shipping for a steal on Ebay; on the other hand, there's a switcher engine on there right now for a starting price of $450, with no takers.
Pre-WW2 is referred to as pre-war; I regard it as nice, but a bit primitive. It's generally cheaper. Post 1950's showed a significant drop in detail and visual quality as the company changed hands, went thru bankruptcy, etc. I don't have any of that, so I can't address functional quality. It's just as pricey as the older stuff---I guess the sellers think that age= value. Best of luck!