Do you think I should look at the AC Hi-Rail, DC Hi-Rail, or DC Scale Northerns?
Since you would be throwing away the circuitry in the AC version in order to install DCC, get the DC version to save a few bucks. My AM Northern has hi-rail wheels, but I have an AM Pacific with scale wheels. This loco does pretty well on code 138 track, including some tight radius curves. I can accommodate hi-rail and scale wheels on my layout, but scale are my first choice so that I have the freedom to run my stuff on scale rail layouts such as our local club's.