I have the K-Line one. I got the K-Line Big Boy first and loved it. Thought it was so massive (It was the largest locomotive I owned at that point.). I liked it so much and hunted down the Allegheny even though I wasn't really that big a fan of them. Both have stock TMCC, and are nice. Don't have the correct number of chuffs or cruse, but nice runners and both stump pullers, and look great with traditional sized and O27 freight. Then I got the Rail King PS-1 Cab Forward. The three of them aren't bad together, but the Cab Forward just does has a better large presence on the rail, nor looks small next to scale reefers. The Cab Forward also has the worst overhang of all three locomotives. Then I got a scale Big Boy, and now they all seem so small.
If you don't have any other large steamers or scale ones (Or scale freight), then the K-Line is a great choice. I've had the K-Line Big Boy run on O27 just fine, so I imagine the Allegheny would too.
If you have scale or other large locomotives (Or scale freight.) get the Rail King version.
