While it seems the OP made up their mind, as promised, here's my take after setting them side by side.
I really like the Rail King allegheny, but I love the K-Line version and here's the break down: when thinking of what to write here what it really came down to was that for models that cost about the same on the secondary market, the K-Line version offers more detail and more features. if you run conventional only it may be less important, but having TMCC and railsounds is a plus for me over the proto 1 on the Rail King version. Electronics aside, the k-line model is much better detailed, especially in the pilot and front of the boiler area, but it also features cab figures and a glowing firebox that looks better than the glow on any of my Lionel locomotives. The K-Line model, while it fells lighter, also feels more sturdy in my hand when picking it up, with the RailKing I've alway felt I needed two hands, one under to keep the trucks from hanging free when lifting it, whereas on the K-Line model I am comfortable lifting with one hand on the boiler casting. Nothing is wiggling, hanging limp, or swinging about. The box reads 1:58 scale on the K-line model and it seems pretty true to scale there, though I didn't compare to the measurements of the prototype. At this size the model does look a little small, especially having seen the real thing up close. In my thinking this is the only real advantage to the Rail-King model. It is not scale to anything in length, but the width and height appear to be proper 1:48 O scale or at least close enough for me. This gives the model a more massive, prototypical look when running beside other o gauge locomotives or heavyweight passenger cars.
All that said, here are some pictures.
Note: The boiler casting on the Rail King model was not screwed in place as I have it apart for repair at the moment. It doesn't affect most of the pictures, but as I was uploading to the computer I noticed in the shots head on of the locomotives that the boiler is cocked to the side. It's not a fault of the model, just of it not being properly attached, sorry about that.
Note 2: right click on pics and open in new window to see full size.
