I like 'em all.
Heavyweights with classy steam power.
Budd, Pullman Standard, ACF streamliners with colorful diesels.
...and the 'Betterment' cars (Heavyweights rebuilt outside and inside into a more modern 'streamliney' appearance.)with either/both.
Unfortunately, the so-called 'Betterment' cars have been more available in that other scale...HO...I once favored. Ergo, there's not much to choose from in O among this category. One of the most glaring omissions in this category (IMHO, of course) is B&O's Cincinnatian. Weaver did a gorgeous model of this engine. The original five-car train, built within B&O's own shops, was a class act that ran two main routes in its troubled lifetime. Although WBB and MTH have made extruded aluminum cars under the Cincinnatian banner, they're nowhere close to the real thing. Key made two runs of this beautiful train in HO brass, one in N scale. You'd think that someone would've made a more affordable version of the train/cars by now in ANY scale (e.g., Fox Valley's Hiawatha in HO and N), but especially O! But, no. It's true that the cars were homegrown and unique to 'the Beano', and would be less acceptable in the usual plethora of roadnames the marketers love to run. (Fodder for rivet-counters, though)
Ah, well, so it goes...
KD