Nitpicking

MTH made an NP Northern?

I have Atlas and MTH reefers.  It seems the MTH are a little hardier to handle, but the Atlas are really nicely detailed.  They are both very nice though.

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Dennis

Hot Water. This is a Railking Imperial NP 4-8-4  # 2626    The original  Timken unit. From the 2010?? catalog  PS-3 wireless tether, nice detail and sound.  The original photos showed 2 Axle trucks but they corrected it to the 3 axle trucks

Well, if it is a Rail King model, then Atlas, Weaver, and MTH Premier Line reefers will all be scale size, and will thus look "bigger" than your locomotive.

The atlas and MTH ones are reasonably close to one another, aside from differences in similar paint colors (MTH's oxide or freight car brown) is a little lighter than atlas. Its been a while since I bought a weaver reefer, but the older ones are going to be obvious. The detail just isnt there. The K-line ones are the same way. The doors on them are just painted on, the crispness of the individual boards in the sides is not the same, etc...

The Atlas have a flat finish and very fine added-on detail. Graphics are crisp and prototypical. The wood grain is quite good. Detailing on the MTH cars is also good, not quite up to Atlas but very nice. Graphics are bolder than the Atlas. The Weaver cars have good graphics, but most of the detail is molded in. The stirrups and ladders are heavier than on the Atlas. They have horizontal brake wheels rather than the stand-up ones that are prototypical on older wooden cars.   Some of the MTH and Weaver graphics are prototypical but many are not, if that matters to you. With Atlas, if they built the car on their own account, the graphics are prototypical or as close as you can get. Custom runs made for clubs and dealers may or may not be prototypical. 

The MTH woodside cars are all 36-footers; Weaver are 40-foot; Atlas makes both. The Atlas and MTH 36-footers are very similar in design, but you can tell them apart at a glance because the MTH finish is shinier. The 36-footer is an earlier prototype than the 40-footer.

The detail on Atlas and MTH cars is fragile, especially the foot stirrups. MTH parts are unobtainable. You can usually get parts from Atlas, but sometimes they go out of stock. Weaver cars are much more rugged, because they don't have the delicate add-on detail. 

I would run Atlas cars with MTH or K-Line 742 series cars. The Weaver cars look better with other Weaver cars. You can run them in a separate train or just make up a block of all Weaver reefers and put something else between them and the Atlas cars to avoid a direct visual comparison. I have a lot of them; I often make up a reefer block or even a whole train of Weaver reefers to take to the club/museum for open house. They are ideal for this purpose; being much less fragile than the others, they are better for carrying around. 

Here are some pictures that may or may not be helpful:

Atlas and K-Line compared. Top row: 40' Atlas on left, 40' K-Line on right.Bottom row: 36' Atlas on left, 40' K-Line on right. The K-Line cars are 742 series, which are very nearly Atlas quality and have interiors. They are much superior to the earlier 762 series reefers, shown in the Western Pacific picture in a previous post. 

An MTH woodside reefer. 

And a Weaver car: