I haven't run any of these,

I haven't run any of these, but I would be inclined to go for the NWSL. I'm pretty sure it's a later run than any of the others (1980 while Akane was run in the 1960s, AristoCraft is from the 1950s, Alco from the late 1970s), and I'm certain that the NWSL it has a can motor. As you point out, you can always put a can motor in, but generally speaking by the 1980s, when brass locos came with can motors they tend to also come with much better gear trains. And NWSL of all folks knew the value of slow speed performance by that time... My experience of Akane's models is that they were pretty typical of their era, with their out-of-the-box slow speed performance being only moderate even when brought back to near-original standard. All of them look pretty good.

Don't forget that while there were only 255 0-6-0's built under actual orders from the USRA, and there were "USRA" models per above, models were also produced under the various roads that received them, for example the B&O D-30 class consisted of the 30 or so 0-6-0's that they received while under USRA control. There were also models produced under these names (Akane appears in this example). There were also some "USRA copies" purchased by many of the roads that got the original 255 as well as MoPac and W&LE - I don't know enough about the details to be specific, but you might want to look into those as well.

As for comparing to plastic such as the P2K, that is going to depend on your use and perhaps more specifically how you view them (literally and figuratively).

I have a number of pairs of brass and plastic steam locos of the same prototypes (eg Bachmann and NJCB 4-8-2 and 2-6-6-2, Rivarossi and Key 2-6-6-6). Once painted and in motion, they all do a similar job of conveying the scene, of generating the impression if you will. If that's what you value, the plastic models are terrific, and they're almost always easier to get onto DCC/sound even if they weren't built for that. I'm having to unsolder the floor of the tender on a Sunset 2-10-2 to get into it to put backup light and a DCC decoder in it!

If you are primarily an operator, the P2k's switching performance (I have one of the P2k USRA 0-8-0's) is almost laughably better than a stock Akane or Red Ball from the 1960s. The later-vintage brass models, such as an 1977 NJCB 0-10-0 and especially a 1985 Sunset 2-10-2, mostly closed that gap. The Sunset in particular creeps from tie to tie very nicely right out of the box on standard DC.

OTOH, if you look closely at those pairs, the detail on the brass models is generally quite a bit better. Not only is there often more of it, things like piping are literally separate items so have a much greater 3-dimensional look on close inspection. If you're into looking at them closely, and especially for closeup photography, the brass models—usually even the oldest ones—generally win the day.

P2K USRA 0-6-0

I can’t recommend the P2K USRA 0-6-0 highly enough; my Rock Island version is factory paint, DCC/sound and will creep along a track at 2 mph. No stalls and sounds great.  I added some weathering and a little light oil in a couple spots on the running gear. 

Vote Aye of P2K 0-6-0

I have painted and DCC serviced a number of these Proto 2000 Heritage series locos.   Well made.  In the eight or so I have worked on for others, one had split gears.   I don't think this problem is endemic to this make and model.

Alternate

As you say you prefer brass --  if you aren't wedded to the USRA version, PFM and I think Overland produced several runs of the Union Pacific 4400-series 0-6-0.  They generally have good running qualities and are easy to find on the second-hand market.

The best USRA 0-6-0 in

The best USRA 0-6-0 in Plastic is The P2K one. Pristine detail, good runner. The only bugbear is limited pulling power. According to my expiences, 13 -13 40' cars are the limit (no trction tires) before it starts to slip.

For brass, the NWSL is the best choice with ALCO Imports the second best. NWSL has a can motor, ALCO a traditional open frame which should be replaced with a modern can motor (coreless coil type). Further all the brass are in urgent need for a improved pick up if you want to do switching duties in earnest with them. Additional wipers to the insulated wheels of loco and tender are mandatory if you want to crawl them over yard ladders. A power pack with capacitors is only the cherry on the cake. In my expieriences they are, applied alone, not the cure-all.

Also mandatory are live frogs of your tracks.

Then they crawl like a dream without hesitation on your yard.

Lutz