I have a fairly large brass collection, probably larger than it needs to be
I generally only buy brass when I can't find what I want in plastic. Unfortunately if you model the SP when I do you don't have much of a choice. My Daylight train is a case in point. I sold my brass Daylight cars when the MTH train came out, though I kept my brass GS locomotive(s) The GS models by Broadway and MTH were not comparable. My Lark train is a mix of brass and plastic cars. Plastic Pullmans mostly, with brass headend cars, a brass diner/lounge/club, and a brass obs. It gets pulled by Plastic E units. Unfortunately it is way too heavy for a single GS!
A big point in favor of brass is layout sized models. Most companies are doing big northerns, articulateds, an so on. Large steamers that struggle on tight radii, or are just plain too big for most layouts. I have those models (guilty!!!
) but I like my 2-6-0's 4-6-0's, 4-6-2's, and 2-8-0's. They look much better on the average layout. A pacific pulling 4 or 5 60 footers is an excellent layout sized passenger train. Unfortunately, they are hard to find in plastic, and nonexistent for the SP. There are a few new 2-8-0's coming out in plastic, but none I can use. IHC did a 2-6-0 that was actually an SP design, but it just didn't pull very well. I haven't found a brass model that I couldn't make run well with a little tuning, mayve a little weight, and if necessary, a careful application of Bullfrog Snot!