I know my ore cars, but more of the Lake Superior type than the Pennsy types. So I can give recommendations on manufacturers.
AHM/IHC - These are equivalent to Tycos. Don't have good detail, don't run very well. These cars have truck mounted horn-hook couplers, and crude running gear. Can be found cheap, and for a reason. If you find one for cheap, it might be useful for modelling a wreck.
MDC - These would be my recommendation. Their detail is not up to the Walthers/Tichy cars, but is suitable, and can be easily upgraded. MDC also makes the most styles of ore cars, both bottom dump and gondola type. The gon types would probably be more appropriate for the Pennsy (I would try to find if they have one prepainted for Pennsy, but due to the Horizon buyout online catalogs are hard to come by). In my experience, the MDC orecars are the best runners. They roll pretty smooth (better if one upgrades to metal wheels), and have negligible tracking problems. Only downside is that they need some painting as the underframe and detail parts are not painted the same as the body.
Walthers - The Walthers standard ore car (no side extensions) would be appropriate for the timeframe that you are modelling. The side extensions (for carrying pelletized iron ore and occasionally aggregates) did not appear until the 1950's-60's, and have only become the norm in the past two decades or so. Walthers orecars have good detail, but have tracking problems. I cannot speak for the new release, which have the metal wheels among other improvements, but all of the past releases have problems with inflexible trucks. The wheels rub the hopper pocket even on tangent track, and have serious problems being pushed through curves and turnouts. The best thing going for the Walthers line is availability: they are in current production and are sold in 12 packs, as compared to 1 or 2 of the other manufacturers'.
Tichy - I only have limited experience with these. These are wood ore cars, appropriate for late 1800s to 1920-1930's. They require assembly and painting, and do look great when done properly. I have not run any Tichy cars, so I cannot comment on their running ability.
My suggestion would be to find the appropriate body type that you need, then buy up as many of those as you can. Ore cars ain't easy to come by, I know.